A guy wakes up next to Kitty's dead body. She has been strangled and there is a visible bruise around her neck. A flashback shows us what happened, it hasn't been a dream.
That night Kitty led him in, took one stocking off and asked him to strangle her as an erotic game. he agreed but then got carried over and didn't stop, turning a game into a real tragedy. Then he started playing with her dead body, ragdolling her on the floor.