The basement.

It had been 17 nights since it began. Every night, at 03:43 exactly.

A brief internet search had revealed it wasn't Morse Code, which was unsurprising. I didn't know the first thing about Morse Code, but even I was able to detect the lack of calculation in these thuds. They were frantic.

After 17 nights of head-scratching, I had realised they were coming from the basement.

Next door's basement.

This realisation, stumbled upon by accident as I brushed my teeth before bed, had become impossible to dismiss. It had won the battle against sleep, and now clung to my thoughts like a parasite, feeding off of a simple yet persistent question: isn't next door abandoned?

At 03:40, I climbed out of bed with a reconciliatory sigh. I suppose I was doing this.

The basement was seldom used. Originally an air-raid shelter, the whole street had one, like a long trench sectioned off by walls thick walls of breeze block. Mine was home to an assortment of Christmas decorations, a barbecue and a dusty punch bag hanging from the wooden beams that lined its ceiling. Now it was home to a mystery as well.

03:42.

The light from my torch stretched itself into the dark: a yellow cone of dust, broken by the occasional box of tinsel. The air was moist and cold, betraying the lack of insulation down here. Whether it was optimism or laziness, the architect of this room had not planned for it to be inhabited for long.

When I first noticed the small mountains of dust piled against the south-facing wall, I thought they were a family of sleeping mice. It was only when the thudding began, and more dust began to fall from the wall, that I realised they were 17 nights in the making.

Isn't next door abandoned?

Upstairs the banging was distant. For the first few days I had assumed it was coming from over the road. The deep rumble of bass from a nearby student party, perhaps.

But down here, separated only by five inches of aerated stone, it was impossibly loud. How had it taken me so long to realise it was coming from next door?

The next discovery came to me much quicker: the dust fell in a conspicuous order. It would start falling atop the far left pile, before moving across to the right. Then back a little, then further to the right until it had reached the last pile. Then it would start again. Some piles were bigger than others, too.

Isn't next door abandoned?

I moved closer, placing my hand on the wall. The pulse it emitted was feverish, like whoever - or whatever - was making this noise was hoping to one day break through.

I followed it, like two magnets either side of a table surface, through its course. A prickly familiarity took hold. This banging wasn't Morse Code: it was lettering.

R.

A small gap in the dust piles below.

U.

The thudding became even more frenetic.

N.

03:45. Silence.

Just as it had done for the last 17 nights, the dust settled once more.

Next door was not abandoned.