From the back of the book:
Cutthroats and cannons!
Many a merchant has made his fortune sailing the high seas, transporting goods from one port to another, traded things that are needed for the one thing he needs: gold. One such man is the powerful sea-trade merchant Baldrick Mornstar, master of a fleet of cargo-laden ships.
When the shipping lanes Mornstar depends on become infested with human sharks, the well-heeled merchant casts about for some brave souls to take care of the problem — permanently. After numerous attempts by hired scoundrels to deal with the pirates on their own watery turf fail miserably, Baldrick decides the best way to end the problem is to catch the blackguards off-guard, hitting them where they're sure to expect it least: at their land base.
Like the town crier Mornstar hired shouts, this is a job for stalwart adventurers, for competent adventurers, but mostly for adventurers who aren't afraid to use their heads. After all, when you're dealing with scurvy dogs like these, it's use 'em or lose 'em.