The timer’s at thirty minutes. That setting kept me synchronized with the Plan. But I’m running late, and I’ve made no allowance for that. Does it matter? I search my brain, trying to order the events of the next half-hour. It’s a mess. I should be at my piano lesson – I’m already late. I’m not sure I have enough time now to get over to Miss Morgan’s room in the main building, to show willing, to feign illness, to leave school. But, if I bunk off the lesson, she’ll come looking for me – I’ve forgotten three this term, and every time she’s turned up at my classroom to remind me. I can’t excuse myself by telling Mr Clark I have a piano lesson only for her to turn up, asking where I am. And I certainly can’t have her caught in the blast. She is not involved in this. I am not a murderer.

I’m only two minutes late for her lesson right now. If I get out of here quickly, that part of the Plan still stands. But we’ll be late for the train. My racing brain isn’t capable of the basic arithmetic necessary to correct the timings. Perhaps it doesn’t matter.

I think the trains run every ten minutes. It could be every half an hour. I’m sure it’s every ten. Every ten would be fine.

I could just reduce the timer to five or ten minutes. Screw the piano lesson. Just run. But the device is armed – it’s volatile. Someone might notice this time. And I’d be setting it for just the moment when Miss Morgan is most likely to come looking.

Will they just sit here and wait for Mr Foxton? For a full thirty minutes? I glance around. Mr Clark has them settling in. They’ll stay here – I’m sure of it.

Make a decision. I am in control here.

No. The Plan stands. It’s been weeks of work – it’s not up for negotiation now. The train, or at least a train, will be there. It’ll be fine.

I grab the handle of the holdall containing my change of clothes, my money, the hotel reservation. Right now, I need to leave.

2.39 p.m.

I turn past the red industrial bins overflowing with leaking bags of food waste, and I stop for a moment, catching my breath from the run over here. I’m behind the original school building, built over a century ago. The ground floor is now the canteen kitchens, the second floor given over to staff offices. I look up to the towering gabled roof. Miss Morgan’s teaching room is up there in the attic. She’s probably watching me right now from the tiny four-pane window tucked between the triangle of flaking facia boards high above me.