I sneak back into Castle Airlie through the door to the larder and up the back stairs. I can hear Moira in the kitchen clattering pans around, but I manage to avoid her, and the back stairs are carpeted with an old drugget that muffles my footsteps. I reach the second floor without bumping into anyone, and gingerly push open the baize-covered door that leads onto the main corridor.

It creaks open gently, and I slip through it, easing it back into place. Still there’s no one about: the house feels eerily deserted. I nip down the corridor to the far end, where Catriona’s room is situated. Several knocks on the door, and no answer. I turn the handle and walk in, not wanting to call Catriona’s name in case she’s nearby and I alert her attention.

She’s not there. I close the door quietly and dash across the room, throwing open Catriona’s huge antique wardrobe, which is almost as big as my whole room back at Aunt Gwen’s. She showed me its contents briefly yesterday evening, but I didn’t get a close look at anything, just enough to admire the shoe racks built on one side, the long clothes rails, and the shelves on the other side with handbags and other accessories neatly arranged. Catriona actually doesn’t have that many things, not like Lucy, who I bet has brimming drawers and cupboards stuffed full with designer gear. So it’s easy to find what I’m looking for on the handbag shelves.

There it is: a Marc Jacobs bag, chestnut, leather, with a big limited-edition buckle with MJ on it, barrel-shaped, with two big side straps. I pull it out and rummage inside. I wasn’t really expecting to find Dan’s EpiPen inside it, and of course, it’s not there. But there’s other stuff. A lipstick. Some mint breath fresheners. One broken earring. A small folded London A–Z map. A postcard from someone called Fitz, sent from holiday in Sardinia. A paperback book called The Fountainhead, with a folded piece of paper serving as a bookmark. I open the book and pull out the paper, just to be thorough. On it is written:

Cat——want this bag? That bitch Plum just bought it too. I’ve only had it two weeks! God, I hate her! Keep it if you want or just give it to the charity shop in Airlie, I don’t care. So pissed off. Luce x x

I turn the paper over. It’s a receipt for a facial, and the salon where Lucy had it done has written in the date of her treatment. I do a lightning-quick calculation: almost a month before Dan’s death. I can’t imagine Lucy keeps old receipts for any length of time—she’d just chuck them out rather than have them cluttering up her pockets. So she must have written this note shortly after the date on the receipt. Which means she gave the bag to Catriona weeks before the night of Nadia’s party.

I reconstruct the chronology. Lucy bought the bag, and doubtless showed it round to everyone she knew, excited about having the very latest, limited-edition, featured-in-all-the-magazines It-bag. Lizzie would certainly have noticed instantly that Lucy was the owner of the newest Marc Jacobs, even without being told: Lizzie has an encyclopedic memory for fashion trivia.

But then Plum managed to secure one too, and that made Lucy so angry that she gave the bag to Catriona rather than have the same one as Plum. (Lucy, I note in passing, must be absolutely loaded—because that bag must have cost a fortune, and if it was barely used, she could have sold it on eBay and got back most of what she paid for it.)

So, on the night of Nadia’s party, the bag was in Catriona’s possession.

I turn the bag over and examine it. It’s a dark chestnut, glossy and polished, its flap decorated with gold studs. There are studs underneath, as well, so it doesn’t get dirty when you put it down: the studs touch whatever surface you put it on, not the leather. So the underside is smooth and unstained.

But I can’t say the same for the back of the bag. You have to look closely to see it, because the stain is small and faint and not much darker than the brown color of the leather, but it’s definitely there. It’s seeped into the leather enough that I don’t think it would be possible to get it out now. I put my fingers inside and probe the lining of the bag. It’s a pale beige material, but when I work my hand down to the place where the outer leather is stained, and pull out the lining, I can see that there’s a much bigger stain on it. It looks greasy. There’s some white residue around it, as if someone’s unsuccessfully tried to clean it. I put my nose to it and sniff, but there’s no smell. I didn’t really expect one from six months ago, but I thought I should try anyway.

Grease. Oil. Peanut oil. I think about the bottle of peanut oil I found hidden in a cupboard, tucked away behind the bar at Nadia’s flat. Someone brought in that bottle of peanut oil, so they could poison the crisps they hoped Dan would eat. And they left the bottle in the cupboard, because they couldn’t risk the oil being found in their possession in case their plan went wrong. I stretch out the mouth of the Marc Jacobs bag, confirming that, as I thought, there’s plenty of room to put a bottle of peanut oil inside. And if it were to have tipped over in the bag, and the plastic seal wasn’t perfect, it might have leaked a little from its neck, and some oil might have seeped out. Enough to stain the lining, and to leak through and stain the leather, too. Proof, if someone analyzes this stain, that peanut oil was carried in this handbag.

I wonder whether whoever brought in that bottle of peanut oil wiped it clean afterward. At the time I thought they must have. But it would still be worth checking, if the police will take this seriously. And maybe, now that I’m accumulating all this evidence, they will.  .  .  .

Just then I hear a noise outside in the corridor, and I jump about a foot in the air with shock. Slipping the bag back onto the shelf, I close the door, shoving the note into my jeans pocket. I look round me frantically for somewhere to hide. Next to the wardrobe is the door to Catriona’s study: I slip in there, leaving the door open a crack, and put my eye to it.

The bedroom door opens, and someone comes in. Oh God, it’s Catriona! I back away from the door, wondering if I’ll be able to hide behind it if she comes into her study, hoping she isn’t going to stay in her room for long.  .  .  . Then I notice that her walk seems oddly wobbly. She crosses the room to the window, and as she turns to look out of it, I realize to my great relief that it’s not Catriona after all. It’s Mrs. McAndrew, back from church. They’re so alike—the red hair, the slim build—but it’s creepy to see what you think is a twenty-year-old and then notice all the lines and wrinkles on her face, like a horror movie where someone ages before your eyes.

“Catriona?” she says, but not as if she’s expecting to find her daughter here. It’s like she’s asking a question to which she already knows the answer.

There’s that same oddness in her voice that I noticed before, out on the drawbridge. Now, without her husband offering her his arm, she wobbles and grabs on to the window curtain to catch herself.

Oh my God. I think Mrs. McAndrew is drunk.

“Catriona,” she says again, and then she starts crying.

I duck my head. The sight of her grief is too much for me. Has inviting me here to Castle Airlie tipped Mrs. McAndrew over the edge? I feel incredibly guilty. I want to go up to her and give her a hug, let her cry on my shoulder, but the shock of me appearing in what she thinks is an empty room might make things even worse. I’m probably the last person she wants to see, anyway. I’m a walking reminder of how her son died—in mysterious circumstances that must make it even harder for her to bear.

Though if Taylor and I are right in our theory of who killed Dan, and why, probably the only thing worse for Mrs. McAndrew than his death remaining a mystery would be for her to learn the truth behind it.  .  .  .

I hear movement, and look back through the partly opened door into the bedroom. Mrs. McAndrew’s making her way back across the room, stumbling as she goes. She stops in front of the door to the corridor and pulls something out of her pocket.

It’s a hip flask.

She takes a swig from it, wipes her lips, and sighs in satisfaction, slipping the flask back into her trouser pocket again. When she leaves the room, she’s actually walking better, as if whatever she drank has picked her up.

This is really, really sad.

I wait several minutes before easing the door open. Mrs. McAndrew is nowhere in sight. I dash down the main staircase, too impatient to double back to the servants’ stairs, running down it two, three steps at a time. Finding that bag in Catriona’s wardrobe has convinced me more than ever that Callum may be in danger right now. Only, because of the weird layout of Castle Airlie, I end up having to run around two sides of the castle in order to get to the kitchen. I should have taken the back stairs after all.

I’m breathing fast as I burst into the kitchen.

“Moira, have you seen Callum anywhere?” I demand.

Moira looks up at me, startled.

“Scarlett! What are you in such a hurry for, hen?” she asks. “Hold on—I’m just getting the last of this cake batter in the tin.”

She’s holding a big china bowl, tilting it over a metal cake tin with one hand, scraping it with a spatula with the other.

“Chocolate and raspberry,” she says. “Master Callum’s favorite.”

“I need to find him,” I say urgently. “Do you know where he is?”

“He took a gun out after breakfast,” Moira says, opening the iron door of the huge Aga oven. A great rush of heat pours out, but Moira is completely unfazed. She slides in the cake tin and clangs the heavy iron door shut again. “Said he wanted to do some clay-pigeon shooting.”

“Where would he go if he wanted to do that?”

Moira raises her eyebrows, hearing the hurry in my voice. But she doesn’t ask what’s going on, just nods to the kitchen door, saying:

“Out there, turn left, and walk along the cliff. You’ll see the ruins ahead, where the old castle was. The clay-pigeon range’s in front of the old ruined tower. You cannae miss it.”

“Thanks, Moira,” I say, and run for the door.

I’ve never been so glad in my life that I’m fit. I sprint across the concrete bridge and by the time I hit the cliff path I’m running—not a jog, a full-out run. It’s further than I thought, but I keep up my pace, fast and steady. I’d hear my even, panting breathing if it weren’t for the sounds of the waves breaking against the cliff below and the cries of the seagulls circling above my head, or swooping and diving for fish. I can’t hear anything but the sea and the birds, not even the sound of a shotgun firing.

Which doesn’t, of course, mean anything at all.

Eventually I see the first sign of the ruined castle: gray stone, half hidden by a huge oak tree. It’s a tower, as Moira said, and it’s so striking that I stare at it, forgetting to watch my step. I trip over a stone in the path and nearly go flying. I save myself with a huge, awkward jump, landing with both feet.

I stand and survey the tower. I’m almost under it now. And it’s more than a tower, actually: there’s a lot of the old castle that surrounded it remaining, though in a sad condition. Weeds are growing up between the stones, and it looks as if the oak tree is growing much too close to the tower for safety, because one of its branches seems to have grown through one of the walls.

I walk, slower, round the tower, looking up at the existing walls of the old castle. I’m searching for the clay-pigeon range, but before I find it, I hear a shot. From above me.

Birds fly up from where they’ve been hidden in the oak tree, shrieking to one another, their wings flapping loudly.

And my phone buzzes in my pocket. I have an incoming message.

From Taylor.

WHERE R U?

I text back frantically, my fingers shaking from nerves:

TRYING 2 FIND CALLUM

Taylor texts back almost immediately:

N MATCHED PIC FROM SECURITY CAM SENDING NOW

I put the phone on Silent. I’m circling the walls now, looking for the way up into the tower. Finally, a gap in the wall. I dash through it and find myself in a grassy open area which must once have been the main hall of the castle, because still here are the stumps of wide stone pillars, wide enough to hold up a big vaulted ceiling.

And straight ahead of me is the base of the tower.

My phone vibrates against my hip bone. I drag it out and stab a button to see my incoming message. The window opens.

I stare, horrified, at the photo in front of me.

It’s Moira, smiling at me above the stack of dishes she’s carrying.

Moira’s face showed up on Nadia’s security cameras.

Moira was at the party when Dan died.

So how does Catriona fit into this? Maybe Callum isn’t in danger at all. Or is Moira trying to kill Callum too so that Catriona can inherit?

I turn to dash back to Castle Airlie.

And then another shot rings out, high up in the tower. It can’t be Moira up there—no way could she have got here before me, not with me running full-out.

I hesitate. It could be Callum up above, taking aim at birds. There’s a perfectly innocent explanation for those shots. And as long as Callum and Moira don’t meet up, nothing bad can happen. I’ve got to get back to the castle.

I’m just clearing the walls of the old ruin when my phone buzzes again.

SORRY SORRY SENT U WRONG PHOTO HERE’S RIGHT 1

And there’s a photo attached. I click on it, and what I see terrifies me so much I let out a little scream.

It’s not the photo I took of Moira and sent to Nadia, so she could match it against the security camera.

It’s the one of Catriona.

I spin round and run back to the tower so fast I don’t even feel the ground beneath my feet. There’s a dark gap at its base, which, as I near it, resolves itself into a narrow entrance leading to a spiral stone staircase. I start to run up until a loose chip of stone turns beneath the sole of my trainer and tumbles down a couple of stairs. In my state of nerves, it sounds like a wrecking ball crashing through a wall. I stop dead, pressing myself flat against the stone wall behind me, only allowing my breath to ease out slowly, silently, through my nose, though my lungs are gasping for relief.

Above me I hear a voice, but I can’t make out if it’s male or female, let alone identify it. I think I hear footsteps, too, but the tower’s close to the cliff edge, and the noise of the waves beating below us and the plaintive cries of the seagulls are loud enough to make it hard for me to distinguish any other sounds.

Which might work in my favor. I can’t hear what’s going on up there, but hopefully whoever’s up there can’t hear me either.

Steadying my breathing, I proceed up the stairs, taking more care on the crumbling steps. This tower isn’t exactly safe: there are big cracks in the walls. But the steps seem to hold my weight well enough, and I don’t have any choice. I have to keep going up.

Suddenly, a shaft of light strikes down the well of the spiral stairs. I must be near the top. Gingerly, I crouch down and creep up the last few treads. And then I raise my head fractionally, fractionally, till my line of vision is just barely at the level of the floor.

I see feet, first of all. Boots, jeans  .  .  . I tilt my head back, looking up the body. It’s Callum. He’s standing further away from me than I anticipated, and I realize that the tower is only a staircase, that there’s a whole upper level here that I couldn’t see from the ground, probably because it was concealed by the oak trees. Behind him there’s a crumbling stone wall, as far as I can tell. And no wonder it’s light up here—the roof is completely gone. Nothing overhead but sky.

There’s a shotgun propped against the wall next to Callum. His arms are by his sides, but there’s a big window at his back and because of the light pouring through it, I can’t see the expression on his face.

“If this is some kind of joke, it’s sick!” he’s saying, sounding completely incredulous. “I can’t believe you’d do this!”

“It’s not a joke,” comes a voice from behind me. “Just do it, Cal!”

“You’re crazy! You’ve gone completely crazy!”

Callum takes a couple of strides forward, and behind me, a shot rings out. The echoes are deafening in the stone room, and I duck down, clapping my hands over my head, terrified of a ricochet. Callum jumps back again, yelling something that gets lost in the sound of the blast.

It seems to take forever for the noise to die down. I wait till I’m sure that there isn’t a bullet bouncing off the stone before I raise my head again. Callum’s stepped further back, terrified beyond words.

“Just jump, Cal. It’ll all be over before you know it.” Catriona has lunged forward, almost level with the stairs now. I just have to tilt my head to see her. She has a shotgun in her arms, which she is aiming straight at Callum.

“Cat, I don’t understand,” Callum pleads with her, rubbing his hand violently over his skull. “Please tell me what’s going on! Is it some sort of game? If it is, it’s not bloody funny, okay?”

“Jesus, Callum!” Catriona yells. “Don’t make me shoot you!”

“Why? Why would you shoot me?” her brother yells back.

“Because I can only inherit Castle Airlie if you’re dead,” says Catriona furiously. “Even though I’m the oldest of all three of us, I couldn’t inherit, because I’m a girl. Did that never strike you as the most unfair thing in the world? Didn’t it? Or did you just take it for granted that you should get Castle Airlie, because you’re a boy?”

“But Cat, I wasn’t going to get Castle Airlie either,” Callum points out desperately, “because Dan is—was—half an hour older than me. How’s that fair either?”

“I’m older than both of you! Two years older! It should have gone to me!” Catriona screams.

Callum covers his face with his hands. “Jesus, Cat,” he says. “I had no idea you felt this way. I promise, I had no idea. You never said a word.”

“There wouldn’t have been any point,” she says. “It wouldn’t have changed anything. I mentioned it to Dad once, and you know what he said? ‘Girls marry and go to live with their husbands, Cat, that’s how it works’! Well, I’m never leaving Castle Airlie. Never. I’m going to make it perfect, I’m going to do all the work that needs doing and Mum and Dad have neglected all these years—”

“Cat, just put the gun down, okay?” Callum pleads. “You’re not in a good state. Please, put the gun down and let’s talk about this.”

He takes a step toward her, his hand held out.

“I’ll shoot you if you take one more step, Callum,” Catriona snaps. “I swear I will. I’ve gone too far to stop now.”

“What do you mean?” Callum stares at his sister, her eyes filled with rage. “Oh my God—Dan? You couldn’t have. That was an accident, wasn’t it?”

Catriona gives a dry, nasty laugh.

“Right,” she says. “It was an accident, actually, believe it or not. I went along to that party with a whole group of Lucy’s friends, and I put peanut oil on every bowl of crisps I could find. It was so easy.” She makes that awful laugh again. “I just dribbled some oil into each bowl before I poured the crisps—then I stirred them around a bit with my hand so they’d get some trace of oil on them. Nobody even noticed me. I’m not one of their group—and all they wanted to do was drink and smoke and get off their faces as quickly as possible. They couldn’t have cared less what I was doing.”

I hear her shift position slightly, her feet moving on the stone flags.

“They were Dan’s favorite crisps, those blue ones he loved,” she’s saying. “I brought them to the party. I was sure he’d eat some, and of course, as we’ve all been told since the dawn of time, it just took the faintest trace of oil to send Dan into anaphylactic shock, right?”

“But he didn’t,” Callum says faintly.

“That’s right, he didn’t. Scarlett ate some instead. I saw her at the bar, talking to him. Then, when she kissed him, she still had some peanut oil in her mouth, and that was enough to trigger the shock. Amazing, isn’t it? It made things so much easier for me,” she adds. “All eyes were on her. No one even looked at the crisps. I couldn’t have planned it better.”

“Cat—” Callum starts. His voice sounds awful now, rough with shock.

“And this’ll be an accident, too,” Catriona interrupts. “You were up here shooting and the floor gave way by the window. It’s all crumbling anyway, everyone will believe that.”

“And what if I don’t jump?” Callum asks hoarsely, sounding so doubtful that I can tell he still doesn’t believe she’ll make him do it.

“Then I’ll shoot you, like I said, and leave you to bleed out. Make it look like you tripped and shot yourself with your own gun. That’ll be a much nastier death, Cal. I’d jump if I were you.”

“No one will believe I’d be that clumsy,” Callum says furiously.

“What else are they going to think? That I shot you?” She laughs, a bitter laugh quite devoid of any amusement. “Come on, I’ll be their only child left. They’d believe anything before they’d think I killed you and Dan!”

“You won’t get the castle anyway, Cat, even if I do jump,” Callum says, sounding frantic now.

“Oh, yes I will,” Catriona says coldly. “There’s a clause in the deed of trust. If all the male heirs die before they attain their majority, Castle Airlie passes to any surviving sisters. I only realized it six months ago, but I started making plans straightaway. I had to get it done before your eighteenth birthdays.”

She takes another step toward Callum. If she’s going to make it seem that he shot himself by accident, she’ll need to shoot him at close range. And that’s going to bring her close enough to me that I could reach out and grab her ankle. I weigh the odds.

If I knock her over, the gun could go off and any of us could get shot. But if I don’t, she’ll kill Callum.

Callum may still have some doubts about the seriousness of Catriona’s resolve to kill him. I don’t. Callum’s brother, Dan, died in my arms. I know, more than anyone, that Catriona’s already murdered one brother.

She won’t hesitate to kill Callum now.

I have to take the risk.

I raise my right arm and snake it out across the floor, reaching for Catriona’s ankle. But just as my fingers touch her boot, she takes another step. I make a grab for her and miss by a fraction. I fall sprawling onto the cold stone as Catriona fires the gun. The blast is so close it’s like something slamming into my head. My brain is spinning with the reverberations. When I snap my eyes open again, I see dust hanging in the air, fine stone chips from where Catriona fired and a ricochet hit the floor.

But I don’t see Callum. Just the empty air where he was standing.

A terrible scream bounces off the crumbling walls and flies into the air.

It’s me. I’m the one who’s screaming.