Counterstrike is a British science fiction television series produced by the BBC in 1969. The series starred Jon Finch as an alien living on Earth as a human named Simon King. He was assigned to live there to prevent an alien invasion of the planet. The programme lasted for one series of ten episodes, but only nine episodes were actually transmitted. The screening of the sixth episode, "Out of Mind", was canceled on the day it was due to be shown due to a late schedule change, being replaced by a documentary on the Kray brothers who had been refused leave to appeal against their prison sentences on that same day. For reasons that will probably never be known, "Out of Mind" was never rescheduled; it was subsequently wiped from the BBC Archives and has never been screened – thus making it possibly one of the rarest pieces of British science fiction television. The first four episodes – "King's Gambit", "Joker's One", "On Ice" and "Nocturne" – still exist in the BBC Archives as 16mm Black & White Film telerecordings, while the remaining five transmitted instalments – "Monolith", "The Lemming Syndrome", "Backlash", "All That Glisters" and "The Mutant" – are listed as missing by the Lost Shows website.