A story

S. was pleased with her new flat on Finchley Road. It would be the first time she would be living by herself. Away from gossipy, tiresome room mates, she would be able to eat whenever she wanted, decide when to bother with the dishes (if at all) and listen to the music that she wanted to without having to ask anyone else first.
"It's a bit cold in here," S.'s friend, M. said when she entered the living room, two days after S. had moved in, peeking behind the open curtains.
"You'll need to crank up the heating a bit."
"But it's already on 'high'," S. said.

She invited a couple of friends to dinner at the flat. They came promptly at 8pm and brought warm fried rice, meat stews and chocolate, as well as several bottles of red wine. After the meal, the men sat around the windowsill, smoking. S. went over to join them.
"Aren't you coming to smoke?" she asked M. M. shook her head, and said, "I like it better on the sofa."
"Me too!" chirped one of the other girls who had been sitting next to M. All four girls were sitting on the sofa.

S's boyfriend P. stayed the night.

When P. went to brush his teeth, S. remembered she had forgot to buy him a toothbrush, so she hurried after him into the corridor leading to the bathroom. She saw him going in so she called out, "P., you'll just have to use my toothbrush, I forgot to buy you one when I went shopping earlier, I'm sorry."
"It's ok," P. said. S. jumped, then shrieked. P. was lying on her bed, in the bedroom, which was fine. Only the bedroom was to her immediate left, not at the end of the corridor where the bathroom was.
"What's wrong?" P. asked.
"Nothing. I thought I just saw you go into the bathroom," S. said. P. shrugged.

Two days later, S. thought she saw something out of the corner of her eye when she was reading in the living room. It appeared to be a shadow, but it disappeared when she tried to focus on it. S. shook her head and carried on reading One Thousand Secret Senses on the sofa until the evening.

A week later, S. dreamt that she was talking to a girl. Someone she didn't know. She was trying to console the girl who was crying miserably. In the morning S. didn't remember the dream but she spent the whole day sitting on the sofa feeling depressed. She sat there looking out at the traffic on Finchley Road until P. called in the evening.
"I had a dream last night," P. said, "I dreamt that you were crying and I was trying to cheer you up. We were sitting on the sofa at your place."
S. felt a vague memory of her dream stirring in her mind.
"That's funny. I dreamt that I was cheering up someone else, sitting on the sofa last night," S. said. They agreed it was very strange.

Soon after that, S. began to feel frequently weak and depressed. She spent most days on the sofa waiting for P. who became very concerned at her apparently fragile state. She whiled away hours during the day looking down on Finchley Road from the sofa, wrapped up in a blanket against the coldness of the living room. P. started to invite her friends over for dinner more often in an attempt to cheer her up. She would greet them from the sofa.

One day P. and M. brought back someone she knew only vaguely from school.
"She's psychic," M. said when the girl had gone to the bathroom, "honestly. We thought it would be entertaining for you. She might be able to tell you your future. She can see things other people can't."
The girl came back from the bathroom and M. shut up.
"Did you know someone died here before you moved in?" the girl asked S.
"What? What do you mean?" everyone asked. S. remained silent, but she looked at the girl questioningly, glaring at her.
"A girl used to live here. She became ill and died, but her soul hasn't left the flat," the girl said.
"That's not funny, stop kidding," S. said, "I live here, you know."
"She is here, too," the girl said.
"How do you know?" S. asked. The girl said, "I can see her. I saw her in the bathroom. She's sitting next to you now." She pointed to the empty space next to S. on the sofa.

P. helped S. move out to his bedsit in Willesden Green that very night.

...based on a 'true' story as told to me by N.. I've seen The Flat (only from the outside, from Finchley Road, of course).