Flat 6B Has a Tenant the Landlord Can't Evict

I rent the top-floor flat, 6B, and it has a small second bedroom I don't use — I work from the living room and the box room became a place I shut the door on rather than fill. That shut door is the start of everything.

It opens. Not dramatically — I've never seen it move, never heard a latch. But every few weeks, most reliably after I've been away even a single night, I come home to find it standing open, six inches or a foot, into a room that is measurably colder than the rest of the flat. I bought a cheap sensor thermometer for it after the third time, out of a need to prove myself either sane or not: the box room runs three to five degrees below the hallway, consistently, on the open-door days. On normal days it matches the flat.

The building is old, converted from a townhouse, and I told myself: draughts, warped door, pressure differentials, the ordinary physics of old conversions. Then the specifics started refusing to fit. The door only opens INWARD, toward the cold; a draught strong enough to swing it would have to blow from inside a sealed room. It only opens when I'm out, never while I'm home to see it, as if it's shy or as if it's polite. And on two occasions the open room contained a smell — pipe tobacco, unmistakable, in a strictly non-smoking building, in a flat where I've never known a smoker.