This is slightly based on H.P. Lovecraft's short story, Cool Air.
It was a small, rather nice and well kept apartment complex, and Jack had gotten a new neighbor. An attractive woman named Casey with red hair and a nice figure. He'd only seen her once or twice at a passing glance, and only during work. The apartment she was using now used to belong to old Mr. Bengs, but he so suddenly moved out that no one got to say goodbye to the old boy.
Jack didn't notice until after two days that a smell had been coming from the room, maybe an animal died in there or something. After day four and his third time running into her in the hall, Jack finally asked to take her for a drink.
They had fun and actually decided to do it again in a few days, which meant good things for him, having not been with anyone for so long. Back in the hall after dropping her off, he caught wind of the smell again that seemed to be coming from her room, stronger this time. He paid it no mind and went about his week.
On into the middle of week two, his landlord informed him of three other people moving out just as suddenly as Bengs. Apparently even the landlord didn't see them go and apparently it was because of the stink, which by the way they couldn't find the source of.
Too bad that people Jack knew for months were all leaving, but it was odd that Casey was the one to tell the landlord of their moving out. Once again, little attention was paid as his work ate too much of his time.
During the third week, the stink was even stronger and now everyone had moved out. It was so strong now that Jack was worried about Casey breathing in whatever it was. When his knuckle hit the door in a knocking motion, the door cracked open, allowing a hot gust of rank air to hit him in the face. The door opened completely and revealed a room with all the furniture the old man had when he lived there, but aged considerably because of this warm and humid air.
Everything was in the same places, but there was an extra lock on the bathroom door and the smell was the worst there. He got a hammer from the kitchen, the old man was kind of odd, and ripped the lock open to find all the people that had "moved out" dead and partially eaten inside.
Jack held his lunch down and found Casey laying on the bed in the next room, completely motionless and when he checked her pulse, dead. He started to panic and sweat, then her eyes flashed open and the last thing he saw was her mouth going for his face hungrily.
Next week, the landlord decided to visit, only to find Jack in the bathroom.