"Many areas of London might be under water for days. For example, the Isle of Dogs could be under eight feet of water for six days. River engineers believe that it is not a matter of if there is a flood, but when the flood comes." (Greater London Council)
An energy drain traps the Third Doctor and Sarah Jane Smith on the planet Exxilon with its hostile natives, causing the travellers to make an uneasy alliance with a Marine Space Corps expedition and a squadron of Daleks. The key to escape for all of them lies at the heart of a powerful and mysterious lost city, but only after a series of deadly traps.
