Retief's Ransom — Keith Laumer

Lumbaga is a planet without known virtues - but with some decidedly odd natives. For every Lumbagan is simply an arbitrary assortment of semi-independent organs inspired by a lust for mayhem. But even the most undesirable chunk of galactic real estate attracts its quota of rival overlords, and the fiendish Groaci had a scheme for absorbing Lumbaga into their sphere of influence. It was working well, too, until it involved Retief, Terran diplomat extraordinary. To his powerful intellect, the machinations of the Groaci were child's play...