When down and out private inquisitor Conrad Metcalf's last client turns up dead, Metcalf takes up the case to find out who killed him. Can he find the killer before he runs out of karma and winds up in the deep freeze?
If Raymond Chandler and Philip K. Dick spent an evening together doing hard drugs, this would be the book that would result. Lethem weaves together the sci-fi and noir elements together so tightly that an evolved kangaroo doesn't seem out of place after his first appearance.
The world of Gun, with Occasional Music, is a bleak totalitarian version of a future California. A future where everyone carries cards noting how much karma they have. When you run out of karma, you wind up in deep freeze for a period of years. A scientist named Twostrand invented a process to create evolved bipedal animals out of ordinary ones like kittens, kangaroos and sheep. Eventually the process was tried on babies, creating the grotestque babyheads. Almost everyone is addicted to a free drug called make that's used to keep the populace under control. Interested yet?
Metcalf's case is a pretty standard one but Lethem injects it with freshness. Metcalf is the prototypical noir private eye with a self-deprecating sense of humor. More than once, he congratulates himself on his use of metaphor. Gun, with Occasional Music, reminds me of the movie Hot Fuzz in that it's both a satire of noir and also one of the better 30's style noir novels I've read in recent memory, much like Hot Fuzz was for action movies. You wouldn't think that a book featuring a gun-toting kangaroo would be a good example of noir but the proof is in the pudding.
I'd recommend Gun, with Occasional to fans of noir, bizarro, Philip K. Dick, and other strangeness.