Mostly Harmless - Plot Summary

Plot Summary

After the events in So Long, and Thanks for All the Fish, Arthur Dent and his love interest Fenchurch attempt to sightsee across the Galaxy, but when Fenchurch disappears during a hyperspace jump due to being from an unstable sector of the Galaxy, Arthur becomes depressed and travels the Galaxy alone, raising money to pay his passage by donating his biological material to DNA banks (mostly sperm, due to it having the highest payout). He is aware that he cannot die until he visits Stavromula Beta, as was revealed in Life, the Universe and Everything, by the insane Agrajag. During one journey, his ship crash lands on the planet Lamuella; Arthur survives and finds a simple life, becoming the sandwich maker for the local population.

Meanwhile, Ford Prefect has returned to the offices of the Hitchhikers' Guide, and is annoyed to find out the original publishing company, Megadodo Publications, has been taken over by InfiniDim Enterprises. Ford discovers that Vogons are part of the Guide's employ, and attempts to escape the building. During this attempt, he finds the Hitchhiker's Guide Mk. II, which he steals and sends to himself, care of Arthur, for safekeeping. Arthur, as Ford had expected, stores the package away without even opening it and forgets about it.

One day, Trillian arrives on Lamuella, and presents Arthur with Random Dent, a teenage girl she claims is his daughter, conceived by Trillian via artificial insemination using the only human sperm samples available, those given by Arthur to pay for his space travels. Trillian leaves Random with Arthur so that she can better pursue her new career as an intergalactic reporter. Random finds life on Lamuella boring and cannot get along with Arthur, and comes across the Guide Mk. II. With Random as its owner, the Guide helps her to escape the planet to find her mother. Ford appears shortly after, looking for the Guide. Together, Ford and Arthur manage to leave the planet and return to Earth, realizing that Random has also returned there. Ford also realizes that the Guide Mk. II, being capable of both time-travel and looking into alternate universes, is manipulating events in accordance with an unknown plan.

Meanwhile, on Earth, an alternative version of Trillian, reporter Tricia McMillan, who never was able to take Zaphod Beeblebrox's offer to travel in space due to wanting to get her handbag, finds herself approached by an extraterrestrial species calling themselves the Grebulons. They reveal that they have set up a base on Rupert (a tenth planet just beyond the orbit of Pluto) after arriving in the Solar System and finding that their computer core and most of their memories had been damaged, and have been following the remaining portions of their mission statement to observe the most interesting things in the system. They have approached Tricia to help them adapt the astrology charts to use Rupert as their base, offering to let her interview them on their base in exchange for the help. Tricia performs the interview but finds that the results look questionable. She is then called to report on a spaceship landing in the middle of London.

Tricia finds Random leaving the ship, and the girl believes Tricia to be her mother, and starts yelling at her. Tricia, with the help of Arthur, Ford, and Trillian, manage to take Random to a bar (address number 42) to try to talk to her. However, she fires a weapon at Arthur; Arthur ducks and the shot kills a man behind him. Ford points out to Arthur that the name of the bar they're in is "Stavro Mueller's Beta", the man just killed being another form of Agrajag, and that Arthur's life is no longer safe, a point at which Arthur takes relief. Shortly afterward, the Grebulons, believing that it would be a positive action to improve their situation, fire upon and destroy the Earth.

It is revealed that the Guide Mk. II was created by the Vogons to complete the destruction of the Earth in every possible dimension, using reverse temporal engineering to bring Arthur, Ford, Trillian, and Random together on Earth for its destruction by the Vogons. After the Earth is destroyed, the Guide collapses in on itself.