Red Dwarf Season 7 Episode 6

Searching for a new head for Kryten (which exploded due to an incident involving ketchup and lobster), the crew encounter a rogue simulant on a deserted ship. The simulant kidnaps Kryten and commissions one of his own droids, Able, to fix him up. But Kryten and Able discover they're brothers, the same model, and Able helps Kryten escape. But not before Kryten discovers a disturbing secret about his creation.