A nuclear reactor is about to turn a large chunk of Britain hotter than a vindaloo, so who do they call in to save the day? The local plumber, of course. Needless to say, that's you and your job as a plumber is to tighten all the joints in the pipes of the reactor cooling system.
There are four pipes on four levels of the screen, each with five joints which have to be tightened with your spanner if they start leaking. The water collects at the bottom of the screen and you can only spend so much time submerged.
Giant mutated rats are flushed out by the water and you can kick these to stop them killing you. The earthquake that started the trouble is still going and the occasional chunk of debris will drop from the ceiling and kill you if you get in the way.