The fourth book in DouglasAdams HitchhikersGuideToTheGalaxy trilogy.

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If you like tidy endings and warm fuzzy feelings, this is the "last" book in the "trilogy" (so, really, what do you call a five-book series??).

If you prefer the pain of seeing where Adams took it before repenting, then read also "MostlyHarmless."  I wish I'd stopped at SoLongAndThanksForAllTheFish -- Adams died before he could repair the damage from "MostlyHarmless."  See editorial remarks in his (sort of) final work, TheSalmonOfDoubt.

And then just don't read MostlyHarmless.

And while you're at it, don't think of an elephant.