The scariest thing that ever happened to me has to be when I was working as a night security guard in this huge old office block. I’d work eleven at night till six in the morning. I had a comfy swivel chair, some monitors to watch and only myself to please for seven hours.

That night I had my book and a flask of coffee to keep me awake and I settled in for the shift.

So far, so normal.

Then, just after eleven, someone called the lift from one of the floors above. Now I was meant to be the only person there, but it was an old building; sometimes electrics played up. I wasn’t panicking.

Eventually it came to a halt on floor 12. I frowned, made a note of it to let my supervisor know, then I checked the monitor that covered that floor, just to be sure.

Strangely, as I looked, that screen flickered and conked out, which made me wonder. If someone had broken in somehow and had made it up to floor 12 then disabled the camera it was my job to stop them.

But why call the lift? It didn’t make sense.

I hauled myself to my feet, grabbed my flashlight and set off up the stairs. By floor 12 I was sweating. The strip lights in the corridor were all still on and I shone my flashlight cursorily into the dark rooms along it.

When I reached the lift things started to get weird.

The lift doors had been propped open with an office chair and the inside of it was completely drenched, like someone had emptied a bucket of water into it.

Wet footprints tracked away from the lift and up the corridor, away from the direction I’d come.

Clearly I wasn't alone.I knew I should go back to my desk and call for support, but I was intrigued.

I followed the footprints.

In the middle of the corridor they just stopped, as though the person had disappeared into thin air. I stopped too and looked around. At the edge of my awareness I heard an infinitesimal click, as though a nearby door had just been closed quietly.

Then, behind me, I heard the lift start up again.

I sprinted back towards it - how could it move? The doors had been wedged open…

I threw myself down the stairs and back to my desk to call for support. This was too weird. The lift was still making its clanking, whirring noises when I reached the ground floor.

But when I reached the foyer, I saw wet footprints tracking their way towards my swivel chair and the monitor for floor 12 flickering to life.

On the screen the door to the lift was opening.

I didn’t wait around to see what came out. I left the building, called for support on my mobile and never went back in.

No-on was ever found in the building. By the time support arrived the footprints had dried and everyone assumed I’d gotten over excited.

They did find an office chair in the middle of a corridor on floor 12 though.

After that I stuck to daytime jobs.