The fourth season of British science fiction television series Doctor Who began on 10 September 1966 with the First Doctor (William Hartnell) story The Smugglers and, after a change of lead actor (Patrick Troughton) part-way through the series, ended on 1 July 1967 with The Evil of the Daleks. For the first time, the entire main cast changed over the course of a single season (the only other occasion this has happened is during Season 21). Only 10 out of 43 episodes survive in the BBC archives; 33 remain missing. No serials in this season exist in their entirety. However, The Tenth Planet, The Power of the Daleks, The Moonbase, The Macra Terror and The Faceless Ones have currently had their missing episodes (seventeen in total) reconstructed with animation and subsequently have been releas