Lust Lizard of Melancholy Cove by Christopher Moore

The town psychiatrist has decided to switch everybody in Pine Cove, California, from their normal antidepressants to placebos, so naturally—well, to be accurate, artificially—business is booming at the local blues bar. Trouble is, those lonely slide-guitar notes have also attracted a colossal sea beast named Steve with, shall we say, a thing for explosive oil tanker trucks. Suddenly, morose Pine Cove turns libidinous and is hit by a mysterious crime wave, and a beleaguered constable has to fight off his own gonzo appetites to find out what's wrong and what, if anything, to do about it.