As I said they come across many strange peoples. It is a very misleading story full of twists and turns.
The first place they visit is the City of Morphoton seemingly inhabited by a race of gentle people who have everything they need and willingly give all that's desired by the Doctor and Companions. However it's all a hypnotic illusion and they barely escape without being enslaved.
The story goes on like this -- there is an outpost in a jungle where a mad scientist has somehow unlocked the secret of amazingly fast plant growth, creating the jungle. Another place is in snowy mountains with a rogue who attempts to trick the Companions and kill them by stranding them in the blizzard. The final place is a city in which one of the Companions is accidentally implicated in murder.