Planet of Giants was the tenth ever Doctor Who story. The preceding episode, the sixth and final of installment of The Outlaws titled "A Guest for the Gallows" ended with the closing caption "Next Episode: Planet of Giants" and with a cliffhanger in which the fault locator warned of a build up of pressure outside the TARDIS. (PROSE: The Thief of Sherwood)
Behind the scenes
In the real world, Planet of Giants was the ninth Doctor Who story. The fictional story of The Outlaws took its place, taking advantage of the gap in transmission between seasons 1 and 2.