Vestibule

It was the summer of 2000. I was dating a girl I loved. We lived in the city, and my parents lived at their dacha. We'd been living together for about a year. I was a programmer, she was a designer, and we worked mostly from home.

One August evening, a client sent me some information in a program I didn't have and tearfully asked me to get it done by the morning. Since the internet wasn't that developed back then, and local area networks were just a dream, I had to go get a disk from a friend's house two doors away (a 20-minute walk, stopping at a store for coffee and juice). I'll note right away that our apartment has double doors, but the doors aren't right next to each other, but rather have a "vestibule" about a meter wide.

I got dressed and left, locking the door (note that if you lock the door from the outside, you can only open it with the key from the outside or the inside). Returning twenty minutes later, I rang the doorbell, forgetting I'd locked it. Irina (my girlfriend) answered from the other side:

"Vasya, is that you?"

"Yes, Irina, open up."

"I can't, I don't have the keys."

"What do you mean, no keys?"

"I just don't have the keys."

Then I remembered I'd locked the door myself.

When I opened the door, I was confused: Irina was sitting on the shoe rack, quietly crying. I couldn't understand anything. Only after half an hour of conversation and strong tea did I manage to get a more or less coherent story.

According to Irina, five minutes after I left, the doorbell rang. Thinking I'd forgotten something, she ran to the door and asked:

"Vasya, have you forgotten something?"

Silence.

"Vasya, is that you?"

Silence.

 The calls stopped, and Irina, thinking it was her alcoholic neighbors (we live in a less-than-favorable building), decided to go back to her room, but it was no use.

When she tried to open the door from the vestibule into the apartment, she couldn't—the door was locked from the inside. Realizing she didn't have the keys and was alone in the vestibule, she was terrified. She heard doors opening and closing in the apartment, and someone walking around (the laminate flooring I'd recently installed creaked). They went to the bathroom, turned on the water, then went to the kitchen, rattling dishes. Then the TV went off, and silence fell. Then came three knocks on the door from the apartment, and everything went silent. This went on for about five minutes, then Irina had to sit in the vestibule and wait for my return.

My first thoughts: homeless people or drug addicts had climbed in through the window from the balcony, but how? After all, we live on the sixth floor. According to Irina, it didn't look like we'd been robbed, but nothing was missing from the house. Everything was in its place, the only difference being the plugs being pulled from the outlets—I only realized this by the beeping of the home server's UPS...