An alien entity has invaded the TARDIS and rendered The Doctor invisible. The time-travellers step out the door into the realm of the Celestial Toymaker, an eternal and powerful being who sets games and traps for his captured playthings. The Doctor has tangled with him before. The Doctor must now play a logic game with over a thousand moves.
Meanwhile, Steven and Dodo face two dangerous clowns playing blind man’s bluff, then the King and Queen of Hearts, with a Knave and a Joker, who play a game of deadly musical chairs, then Sargent Rugg and Mrs. Wiggs who force them to search a kitchen for the key to escape, then a pair of ballerinas who force them to dance within sight of the TARDIS. They win their way to the TARDIS, but it is a fake. Then they play a game of hopscotch against Cyril the Schoolboy, who falls victim to one of his own booby-traps, and they finally reach the TARDIS.
The Doctor realizes that his last move in his game will make the Toymaker’s world disappear, and the TARDIS will disappear with it, but he tricks the Toymaker and they all escape.
The Toymaker (Michael Gough) made a striking and classy villain, but did not appear much in the story, which was a little lacking in action for the TV Audience. William Hartnell was on vacation during episodes 2 and 3 and did not appear. There was a conspiracy afoot by the producer to replace Hartnell with another actor when The Doctor became visible again, but it was thwarted by the Head of Serials of the BBC, so the producer quit in protest. One wonders if this was the birth of the idea of Doctor regeneration. In the end, Hartnell retired about five stories later. Only the last episode of the serial exists.