When the train pulls into Hampstead I join the crush of bodies surging towards the exit. It’s only 10 a.m. but, according to my phone, the temperature is already in the high twenties. As I reach the top of the stairs the crush intensifies. I put my hand out to grab the rail but before I can get a grip someone shoves me in the small of my back. I lose my footing and half fall down the stairs.

‘Are you all right, dear?’

I look up and see an elderly woman with short grey hair and red lipstick. She is standing above me, holding out her hand.

‘That idiot could have killed you.’

‘Who?’ I whimper, taking her hand and hauling myself up.

‘The man who knocked into you,’ says the woman, shaking her head. ‘He’d already nearly sent me flying as I got off the train. I don’t know, you expect behaviour like that during rush hour but on a Saturday morning – well, it’s just not on. Are you sure you’re okay, dear?’

I tell her that I’m fine, then, as she walks away I stand for a moment to catch my breath. The fall has disorientated me. Then I remember: the bird. I thrust my hand into my bag and, to my relief, find it’s still there, unharmed. The thought of it being crushed under a hundred pairs of feet doesn’t bear thinking about.

I run my fingers along its smooth glass surface, then, taking a deep breath, make my way out of the station and on to the high street.

The sun is baking hot on my back as I cross the road, aware of the volume of people, their eyes watching me. I take a left down a narrow side street and breathe a sigh of relief as I leave the crowds behind.

But as I get closer, my optimism fades. Ahead of me I see a line of police tape sealing off the end of the street. Two patrol cars are parked across the entrance to the house.

I look around. The street is empty. I feel conspicuous. What if Bains is up there? How would I explain my being here? I need to get away. Fast.

I turn on my heels, the weight of the bird and book pressing on my shoulders, but as I reach the bustle of the high street and prepare to join the throng of tourists heading from the station, I tell myself that I have to hold my nerve. I have to finish this.