He gives you a moment to compose yourself, relocking the door, then hands you the big bunch of keys. “These are yours to look after,” he says.

It’s heavy, and there are a lot of keys, of all shapes and sizes, and none of them seem to be identified by words, though some have coloured fobs. You can probably work out what some of them do and make a list to keep with you.

“Get your coat and bag off – filthy night – and I’ll walk you through it.” You follow him to the curved reception desk, and then around behind it. You see that as well as a phone, a computer screen – the base unit is tucked away underneath the counter – and a pot full of biros, there’s a pile of telephone directories, a big rubberised torch sitting on a blue ringbinder, and a little standalone black-and-white television. Next to the TV is a clicky dial, and you realise that it’s a rudimentary CCTV system. You hang your coat from the back of the chair, and put your rucksack down on it.

“First duty,” says Metcalf, “is to make sure the building’s empty, top to bottom. Everybody who’s supposed to be here has gone home already. Start at the top, work your way down – make sure the front door’s locked. Then check the car park.”

He sees you blink, and elaborates. “You walked here. There’s a basement car park, with keycard access. There’s a homeless bloke who tries to get in some times, Davy. He’s harmless enough, but you have to be firm with him. He absolutely can not be allowed to sleep on the premises: if anything happens to him, and he’s old and alcoholic, so it’s quite likely he’s going to pop off soon, we can be held liable. He’ll leave if you’re firm.”

“Even on a night like this?” you ask.

“You have to be firm,” Metcalf repeats. “We can’t risk it. Okay?”

It’s your job now. You hope he’s not managed to sneak in, because you’re not good with confrontation. “I’ll deal with it. Him. I’ll deal with him,” you say, and Metcalf nods approvingly.

“Once you’ve done that, it’s pretty much it for the night. The ground floor and the basement are the obvious points of entry for thieves. Check both every couple of hours, then the rest of your time’s your own.”

“What do I do if something happens?”

He points to the blue folder. “All the phone numbers you need are in that. No stupid heroics, mind. If you find someone inside, or you hear someone breaking in, get to somewhere safe, lock yourself in and call the police. It’s a condemned office block, not the crown bloody jewels. First contractors get here at six: sign the keys over to their gaffer, and go home for some kip.”

He reaches past you for the folder, and after tipping the torch off the cover, flips it open. At the very front, there’s a signing sheet. He writes in the time and the date, prints his name and signs it. Then he gives you the pen so you can do the same. You negotiate the first of your duties successfully enough, and Metcalf flips the folder closed.

“Have a good night,” he says. “May it be entirely uneventful.”

He walks over to the front doors, and waits, tapping his foot lightly on the mat. You realise that you have the keys, and you now are in control of the building, who comes in and crucially, who goes out. You hurry over and with an apology, stare at the bunch of keys in your hand, wondering precisely which one will unlock the doors.

“That one,” says Metcalf, pointing to an unassuming Yale key without a fob.

You peer at it, and see it’s got a serial number stamped on the round part of the steel key: 542. You’ll have to remember that. You push the key home, twist it, and feel a bolt grudgingly move. The wind pops the door open, and Metcalf hunkers down into his coat. “You’ll be fine,” he says as he leaves.

His figure is swallowed up into the rain-washed night, and you relock the door, giving it a shake to make certain it is locked. It seems that way. You go back to the reception desk and take out your book, your flask, your music player and a packet of cheap own-brand biscuits on the desk. You brush the rain from your hair, and look around you. This is it for the next eight hours.

Do you:

Try and work the CCTV?
Pour yourself a cup of coffee and start on the biscuits?
Begin your inspection of the building?