Then something unexpected happens and I am overcome with calm. Although I can hear Graham rattling the door and scuffling outside, there is not a single bit of me, not an atom, that is panicking.

My breathing steadies, and I hear my dad’s voice as if he’s right next to me. I even turn my head slightly in a reflex, to where I hear it, but of course it’s all my imagination. The only noise is the creaking of the wooden broomstick as it resists Graham’s assault.

It’s suddenly clear to me exactly what I have done wrong. The words Dad wrote come back to me:

The laws of spacetime seem to be beautifully arranged to prevent such chaos.

I cannot go back to the same place and time that I was before: it has already been occupied – is already occupied – by me.

With my fingers hitting the keys noisily, I re-type the coordinates, altering the time to an hour later in the day and two things happen simultaneously.

1. I hear a crunch as the broomstick bends and snaps but the remaining pieces are still holding the door shut, just.
2. I see Alan Shearer scampering across the floor of the bunker.

Without thinking, I leap out of the tub, kicking the swivel chair aside, to scoop him up. I shove him in my pocket, grab the laptop and the hand grips, and get back into the zinc tub.

“Did you hear that, Bella? I reckon there’s someone down there!”

The pieces of broomstick finally give up and fall to the floor. The wheel is turning when I press ‘enter’ and the room goes blurry.