Terror of the Zygons

TV Season 13, Serial 1

Aired: 30 August - 20 September 1975

The TARDIS returns to Earth to answer a summons from the Brigadier, making this the last proper UNIT story. Introduces the Zygons. Harry decides to stay behind. This was supposed to be the last story of Season 12, but ended up as the first story of Season 13.