We are in luck. The door to the block isn’t properly latched. I push our way inside, pulling Charlie after me. Inside, there’s a wide, echoing staircase leading upwards. I check the flat number; it looks as if Freya lives many floors up.

We start climbing. The stairs zigzag up and up; the wall on one side of the tower is a floor-to-ceiling window. As we climb I feel a dizzy vertigo, as though the stairs, the walls are tilting, as though I could fall right out of that huge window. As we climb higher, I can see right out into the city. London is out there. Somewhere, across the river, lies my flat; empty, waiting for us to come home. Somewhere out there is the bedsit Sarah lived and died in; somewhere, Alastair is asleep in his bed. Charlie trips on the stair beside me and I jerk up my arm to wrench him back to his feet. I can’t stop now to analyse his clumsiness, I can’t be the one to find the answers any more. I just have to get to the top, and to Freya. We are nearly there; the numbers rise with every floor we reach and we are nearly there at Freya’s door. This high up, I can see a smear of light low down in the sky, in the east. The sight of it brings such a sense of hope. The dawn is coming, the night is almost over.

And now we’re here. The ninth floor, and here is her flat, number twenty-four and the sight of it almost makes me collapse with relief. In my bag, my mobile phone pings. A message has arrived, but who would be texting me at this time in the morning? I drop Charlie’s hand to reach for the bell on Freya’s door.

I press my finger on the buzzer and, at the same time, out of instinct I pull out my phone.

The message is from Chloe. I see her name first; I’ve saved her number in my contacts. She’s on the other side of the world, a whole time difference apart; now the timing of this text makes sense.

I’ve remembered the name of Sarah’s cousin, writes Chloe.

But what does Chloe’s message matter now? I’m not looking for answers any more. I’m going to leave all that behind. I’m going to tell Freya that she was right. I’m so aware of the huge glass window behind me, the pale light shining on the horizon. I press the bell again; I’ve done it now. In a matter of moments, she will wake up and the door will open.