Life, the Universe and Everything (Hitchhiker's Guide to the Galaxy #3) by Douglas Adams

Part three of the Hitchhiker's Guide to the Galaxy trilogy of five books. Featuring exclusive bonus material from the Douglas Adams archives, and an introduction from Simon Brett, producer of the original radio broadcast. In Life, the Universe and Everything, the third book in Douglas Adams' blockbuster sci-fi comedy series, Arthur Dent finds himself enlisted to prevent a galactic war. Following a number of stunning catastrophes, which have involved him being alternately blown up and insulted in ever stranger regions of the Galaxy, Arthur Dent is surprised to find himself living in a cave on prehistoric Earth. However, just as he thinks that things cannot get possibly worse, they suddenly do. An eddy in the space-time continuum lands him, Ford Prefect, and their flying sofa in the middle of the cricket ground at Lord's, just two days before the world is due to be destroyed by the Vogons. Escaping the end of the world for a second time, Arthur, Ford, and their old friend Slartibartfast embark (reluctantly) on a mission to save the whole galaxy from fanatical robots. Not bad for a man in his dressing gown. Follow Arthur Dent's galactic (mis)adventures in the rest of the trilogy with five parts: So Long, and Thanks for All the Fish, and Mostly Harmless.