Past Tense

A former cop who is now a novelist notices an attractive young woman move in next door to him. He strikes up a conversation, one thing leads to another and he spends the night. She asks him to come back the next evening, but when he does he discovers that she has been killed. When he reports the murder, he is told that no such woman ever lived there, and when he gets back to the house there's a completely different woman staying there--who he's never seen before--who claims that she's lived there for years and no other woman has ever lived there.