From Academic Kids
Mostly Harmless (1992, ISBN 0345418778) is a novel by Douglas Adams, the fifth book of the Hitchhiker's Guide to the Galaxy series. It is described on the cover of the first editions as the "fifth book in the increasingly inaccurately named Hitchhiker's Guide to the Galaxy trilogy".
The title comes from a joke early in the series, when Arthur Dent discovers that the entry for Earth in The Hitchhiker's Guide to the Galaxy consists, in its entirety, of the single word "Harmless". His friend Ford Prefect, a contributor to the Guide, assures him that the next edition will contain the article on Earth that Ford has spent the last few years researching—somewhat cut due to space restrictions, but still an improvement. The revised article, he eventually admits, will read "Mostly harmless."
In an interview reprinted in The Salmon of Doubt, Adams expressed dissatisfaction with the "rather bleak" tone of this book, and said that he "would love to end Hitchhiker on a slightly more upbeat note" by writing a sixth installment in the series. He blames personal problems, saying "for all sorts of personal reasons I don't want to go into, I just had a thoroughly miserable year, and I was trying to write a book against that background. And, guess what, it was a rather bleak book!" Nonetheless, the story does a good job of tying together most of the plot elements introduced in the previous novels in a typically quirky way.
Dirk Maggs, who has adapted the book for performance on radio, has indicated that he has modified the ending to make it less bleak and depressing, and to tie in the last three books with the first two radio series. The adaption, named the "Quintessential Phase" will broadcast in June 2005.
Mostly Harmless picks up the story of Arthur Dent some time after the events in So Long And Thanks For All The Fish. Fenchurch, Arthur's love interest in the previous book, does not appear, her absence being explained away in a single paragraph. The plot revolves around the concept of parallel universes (though according to the novel, they're not really parallel universes at all but only a model to capture the continuity of space, time and probability) and the introduction of a new, sentient version of the Hitchhiker's Guide which can perceive, and act upon, all possible universes at once. The book finally fulfils the promise made at the very start of the series that the fates of Arthur and the Guide are intertwined.
The book ends, as the first book began, with the earth being blown to bits. For good, this time.
Being the fifth book in a trilogy it wasn't clear that this was the concluding book in the series until Douglas Adams's death due to a heart attack on May 11, 2001 made it mandatory. Although the complete destruction of every version of the Earth in every possible timeline, along with the death of nearly all the regular characters, would seem to make a continuation extremely unlikely, Adams had expressed an interest in continuing the series, remarking that the afterlife-enhanced state of the regulars merely meant he would not have to waste time at the beginning of the next book gathering them together or explaining what they'd been up to in the intervening period.