It was noted for being the beginning of the end of the Doctor's exile on Earth, with the Doctor's TARDIS still under the control of the Time Lords (The Mutants) and restricted freedom (The Curse of Peladon and The Time Monster), as well as UNIT and the Master appearing less frequently in compared to the previous two series. As well as the return of the Daleks and the Ice Warriors, this series also introduced Alpha Centauri, Aggedor and the Silurians' aquatic cousins the Sea Devils.
