One Night in November

The Fringe Division in the alternate world seek the help of our team to catch a serial killer who is drilling into people's brains and stealing their happy memories. They want to take our world's version of the serial killer – a law-abiding forensics professor - over there to examine the killer's house and offer clues in tracking him down.

The professor agrees to take part in the investigation, but isn't told he is being taken to another world. However, while examining the killer's house, he finds a picture of a farm he recognises and figures out something is amiss. Olivia manages to talk him around and he reveals he had the same urges as the serial killer when younger but was saved by a local woman who taught him to control his blood-lust.

The professor runs away from the team, and tracks down the killer to his childhood farm. By the time the Fringe team reach them, the killer has tapped the professor's brain and witnessed the happy memories that stopped our version of the man becoming a serial killer. The team shoots the serial killer before he can murder his doppelgänger, and return the professor to our world - who luckily has no memory of his experiences on the other side.