Three girls one their way home after a birthday party when the father, who is loading the presents in the back of the car is hit and the car is hijacked by a bald man (James McAvoy) who claims later that he has been stalking them. But he realises that he has to kidnap the third girl who is inadvertently in the car too.
The girls find themselves in a bizarre unclean basement with a strangely clean bathroom. You notice this because the bald guy keeps cleaning up stuff and we know how people with a cleanliness fetish: how come other things are unclean and shabby? Or are other personalities okay with the general mess and he lets them be?
He portrays Hedwig, a nine-year-old (in track pant suit), Patricia (in a skirt and shawl of course) and the stern Kevin seamlessly. He basically saves the film because the shots of his transformation from one personality to another are a treat to watch.