So Long, and Thanks for All the Fish is the fourth book of the Hitchhiker's Guide to the Galaxy "trilogy" written by Douglas Adams. Its title is the message left by the dolphins when they departed Planet Earth just before it was demolished to make way for a hyperspace bypass, as described in The Hitchhiker's Guide to the Galaxy. The phrase has since been adopted by some science fiction fans as a humorous way to say "goodbye" and a song of the same name was featured in the 2005 film adaptation of The Hitchhiker's Guide to the Galaxy.
Arthur Dent has hitch-hiked through the galaxy and is dropped off on a planet in a rainstorm. He realises that he appears to be in England on Earth, even though he saw it destroyed by the Vogons.