‘Your gun,’ says Simon. ‘Let’s talk about that.’ He walks over to the bar area of the restaurant and leans his elbow on it. God, I could do with a drink, though it’s not yet ten in the morning.

‘You used it to shoot your first four victims, and when you weren’t using it, it was here at the Khaybar, safely stowed away.’

‘Here?’ says Kerensa the profiler. ‘In an Indian restaurant? But—’

‘On a hunch, I asked the manager how often you were here,’ Simon tells Isobel. ‘This place used to be Rudolphy’s, I thought – surely you’d still be obsessed with the physical space that your family’s bookshop used to inhabit. Turns out they know Faith Kendell very well at the Khaybar. After every killing, within two or three days, you’d book a table for one and come here for a meal, alone. You did the same before each killing, apart from Marion Hopwood. I got the exact dates from the manager, who keeps records of bookings going back about a year, luckily for us.’

Isobel smiles as one might at someone else’s good news. As if she’s pleased for him.

‘You can all see the seats in the booths.’ Simon looks around the room. ‘Long rectangular cushions set into wood. Each one acts as a kind of lid for the bench it covers, and there’s a hollow space underneath. Isobel, you came here and replaced your gun after each shooting. And you’d retrieve it before the next one. You’re probably assuming it’s where you left it, directly beneath where you’re sitting now, but it’s not. I had it removed two days ago.’

Her face crumples. ‘You shouldn’t have touched it. It wasn’t yours to take.’

‘Where did someone like you – educated middle-class woman who’s interested in books – get a gun?’ Dunning asks her.

‘Derby,’ says Isobel briskly. ‘Being educated and bookish isn’t a barrier to accomplishing practical tasks, you know. It infuriates me when people imply that it is. Without books and the knowledge they contain, we’d none of us know how to exist in the world at all.’

‘Tell us about Derby,’ says Simon.

‘There was a documentary on Channel 4 about a council estate there where little children had guns. That’s where I went. It looked perfect. I paid a lot. It was hard to find a child to buy one from, but I did. I was determined not to compromise and buy one from an adult or even a teenager.’ She smiles suddenly. ‘I had a first edition of a Secret Seven book, you see, and I wanted to give it to whoever I bought the gun from. You have to catch them early.’

‘Who?’ Simon asks.

‘Children. If you want to instill a love of reading.’