The Salmon of Doubt is a collection of previously-unpublished material by Douglas Adams, published after the author's death in 2001. It consists largely of a compilation of essays, most of which have a technological edge, but its major selling point is the inclusion of the novel on which Adams was working when he died (and from which the collection gets its title).
The actual manuscript of the proposed novel is, unfortunately, extremely short and only gives us a glimpse of what The Salmon of Doubt would have been. It is composed of the best content out of several drafts (as were many of Adams' books). The existing plot involves Dirk Gently, the detective protagonist of two earlier Adams novels, refusing to help find half a missing cat (some premonition here...?), receiving large amounts of money from an unknown client, and then flying to the United States, although Adams had not yet decided where to, and at this point the story slows down and ends. As promised in the beginning, we don't go through a rhinoceros.
Curiously, early on in the book Dirk Gently dials his own phone number, and answers his own call. This may have been foreshadowing some sort of time travel later on.
In one of the interviews reprinted in the book, we learn that Adams didn't like the ending he wrote to his Hitchhiker's Guide to the Galaxy trilogy, and that he was thinking of continuing the trilogy in the Salmon of Doubt. However, if this had been planned out, it was not included in the manuscript, which stars Dirk Gently only.
