From amazon.com:
The Sirens of Titan (1959) is Vonnegut's second novel and was on the Hugo ballot with Robert Heinlein's Starship Troopers but lost in what Harlan Ellison has called a monumental injustice. Sirens of Titan is a picaresque novel which almost defies being synposized; it is an interplanetary Candide (lacking perhaps Voltaire's utter bitterness), the book follows lead character Malachi Constant, a feckless but kind-hearted millionaire as he moves through the solar system on his quest for the meaning of all existence.
Constant is aided by another tycoon, Winston Rumfoord, who with the help of aliens has actually discovered the fundamental meaning of life (the retrieval of an alien artifact with an inscribed message of greetings). With the assistance of Salo, an alien root and overseeing the alien race, the Tralmafadorians (who also feature in Slaughterhouse-Five), Constant attempts to find some cosmic sense and order in the face of universal malevolence. Together Constant and Rumfoord deal with the metaphysics of "chrono-synclastic infundibula", they deal with the interference of the Tralmafadorians; the novel is pervaded by a goofy, episodic charm which barely shields the readers (or the characters) from the sense of a large and indifferent universe.
All of Vonnegut's themes and obsessions (which are further developed and/or recycled in later work) are evident here in this novel which is more hopeful than most of Vonnegut's canon. It is suggested that ultimately Constant learns that only it is impossible to learn, and that fate (and the Tralmafodorians) are impenetrable, unavoidable circumstance.
On the basis of this novel, Vonnegut was wholly claimed by the science fiction community (as witnessed by the Hugo nomination), but Vonnegut did not likewise wish to claim the community for himself and the feelings were not reciprocal. He felt from the outset that being identified as a science fiction writer could only limit his audience and trivialize his themes. His recurring character, the hack science fiction writer, Kilgore Trout (who also features in Slaughterhouse-Five), represented to Vonnegut the worst case scenario of the writer he did not wish to become.