So Long, and Thanks for All the Fish

The fourth book in The Hitchhiker's Guide series.

Three years have passed. Arthur hitches a ride to the spot where the Earth once was, and is shocked to find the planet perfectly intact. Arthur hitches a ride with Russell and his siste; Fenchurch, and immediately falls in love with her. The entire world believes that the Vogon fleet was actually a drug induced hallucination and that only three months had passed. Arthur locates the place his cave in prehistoric Earth is currently, and the location turns out to be Fenchurch's house. Arthur and Fenchurch start a romantic relationship. Arthur learns that the dolphins had disappeared at the same time as the Vogons. They learn that the dolphins took an alternate reality version of Earth and placed it where their Earth previously had been.

Ford discovers that the entry he wrote about Earth has suddenly reappeared in his copy of the Guide. Intrigued, he hitchhikes to Earth on a ship commanded by a Giant Robot. Ford runs into Arthur and Fenchurch, who have decided to go to the location of God's Final Message to Creation. It has become a major tourist attraction. Arthur comes across Marvin, who, because of the various time travel he's been through, is now many times older than the Universe itself. Marvin reads the far-away message with Arthur and Fenchurch. The message being "We apologise for the inconvenience”. Amazingly, Marvin says that he feels good about it, and promptly dies in Arthur's arms.