Another entry in the popular but short-lived Hammer TV series. This one features a doppelganger whose presence spells danger for his distraught wife: it's one of the more original episodes of the series, opening with a well-staged car accident and closing with the kind of creepy twist ending that works well in the best old-fashioned way.
The rest of the episode is slightly repetitive but intriguing, as we're left unsure as to whether the put-upon wife really is being haunted by an evil presence or whether she's losing her mind. The physical horror is limited to a long fingernail and a few facial scars on her disturbed husband, but the atmosphere is effectively unsettling and once the story picks up towards the end I was really enjoying it.