The Eternity Game

"Mind Games" is the seventh episode in the ninth season of Doctor Who, and sees the Doctor and Billy being forced to play a dangerous game of wit and survival, controlled by the powerful Castrada.

Synopsis
"The last Time Lord, my latest toy!" - Castrada

Soon after leaving 26th century Earth (Devour) the Doctor and Billy are suddenly transported to a distant planet, where a maze exists, and the extremely powerful Castrada pits various races in his game of endurance, wit, and survival. With the only option to play, Billy and the Doctor soon begin to realise that Castrada’s game is serious, and that the penalty of loosing is death.