The Doctor is turned invisible, inaudible and intangible, and Steve and Dodo clown around in this both childish and completely racist serial.
As The Doctor, Steven and Dodo arrive… somewhere… Doc has been turned invisible and intangible. Then, shortly thereafter, he’s all fine again. It turns out they’ve been kidnapped by the Celestial Toymaker, one of the Guardians of Time (we don’t find that out yet) whose hobby it is to abduct people and make them play childish games, and then transform them into toys if they lose.
The troupe is split up, with Steve and Dodo having to play said games, pinned against such dastardly foes as harmless yet annoying clowns, harmless yet annoying playing cards, a harmless annoying cook, and so on. Meanwhile, The Doctor has to play a game of the Trilogic Game with/against the Toymaker. And Steve and Dodo can only find the TARDIS and leave by continually winning, and the Doctor can only find the TARDIS and leave by, well, that’s never quite established.
Whatever. That’s pretty much it.