Douglas Adams is a . . . NUT. And not of the macadamian variety. Not satisfied with a reputation that has become a byword in science fiction (a word not mentionable in polite society) or for creating a rush on hotel towels--and oh, yes, "The Hitchhiker's Guide to the Galaxy," a must for those extra-terrestrial minded. No-ooo --he has to go write yet a fourth book in his aforementioned trilogy and extend his reputation (and career) even further.
When last we dealt with the peripatetic Arthur Dent (Our Hero) in "Life, the Universe and Everything," he was left with the information that on a certain planet was God's Last Message to His Creation. The message is NOT the title to the book--that's a message from someone else and only good ol' Wonko the Sane of California knows just from whom and to whom it is. And just what it has to do with the rest of the story.
Arthur Dent returns to Earth, to his favorite village pub, confused but glad to be here, since as last he knew, the planet had been previously destroyed by the Vogons to make way for an inter-galactic freeway.
Things get more complicated. Dent meets the girl of his dreams, Fenchurch. He gets his job back with the BBC. Ford Prefect has been trying to ring him for simply ages . He learns how to fly without the aid of a plane or glider, and--all the dolphins have disappeared, but they have left a clue behind. Dent and Fenchurch have an important voyage to make, to read God's Last Message, etc. etc. and well, that would be telling. . . .