Plot? What plot?
The Earth gets blown up and then they go knocking around the galazy, looking for the Meaning of Life, with random interludes of white mice, Brockian Ultra Cricket, tea, the occasional nova, and flying. And Marvin ends up approximately 27 times the age of the universe.
can't forgot Pan Galactic Gargleblasters
"Yes, I can read your mind. It's a wonder you can live in something that small. Makes my head hurt, trying to think down to your level."