London, in the summer heatwave of 1930. The Doctor is visiting with Romana and K9 in order to return some library books, but traces of time pollution may change his plans.

A seaside hut holds a strange secret. A biscuit millionaire is hiring assassins. Deadly butlers and solicitors stalk the streets.

There is an odd smell in the air. And it might just mean the death of everyone on the planet.