Christopher Moore 
Lust Lizard Of Melancholy Cove 
Book 2: Pine Cove Series

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. 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.