10 Scariest Star Trek Episodes Ever

10. Genesis

Star Trek: The Next Generation - Season 7, Episode 19

Comfortably one of the highlights of the Next Generation's often-dismissed Season 7, Genesis is a slice of terrifying monster-horror that wouldn't have been out of place on shows with far darker reputations. Giant beasts, disfigured crewmates, something that's half-Reg Barclay, half aracho-nightmare, the episode saw TNG scoop 10 Emmy nominations for its makeup work that year.

After a torpedo veers wildly off course during a training drill, Picard and Data set off on a short Lads Day Out to retrieve it. When they return to the ship, they find it adrift in space with no sign of the crew and one of the bridge officers physically eviscerated in his seat.

They discover that a reactivated T-Cell in Lt. Barclay has triggered a mutation in the rest of the crew, causing them to de-evolve into more savage lifeforms. Worf, in particular, becomes a nightmarish, armoured hell-demon who rampages through the ship attempting to mate with Troi. A cure is found in Data's cat Spot, but not after some ghoulish scenes had the audience leaping out of their seats and scurrying behind the sofa in equal measure.