Life, the universe and everything - Douglas Adams

In Life, the Universe and Everything, the third title in Douglas Adams' blockbusting sci-fi comedy series, Arthur Dent finds himself enlisted to prevent a galactic war.

In consequence of a number of stunning catastrophes, Arthur Dent is surprised to find himself living in a hideously miserable cave on prehistoric Earth. However, just as he thinks that things cannot get possibly worse, they suddenly do. He discovers that the Galaxy is not only mind-boggingly big and bewildering but also that most of the things that happen in it are staggeringly unfair.