The Witches of Karres

HIS LUCK HAD FINALLY TURNED... ... and for the worse. Unlucky at love, unsuccessful in business, unable to win friends and influence people, Pausert thought he had finally found his niche: captaining the stout old tramp starship VENTURE and her odd-lot cargoes around the fringes of the Empire. He'd even taken to performing the odd noble deed, such as freeing three poor little child-slaves from their abusive masters. Strange, though, how eager those sadistic bullies had been to let them go, and even stranger how quickly those adorable little girls made Pausert the mortal enemy of his fiancee, his planet, the Empire, the Sirians, the Uldunians, the dread pirate chieftain Laes Yango -- and the Worm World, the darkest threat to mankind in all of space. It was all very mysterious -- until Pausert realized that he was dealing not with a trio of underage slaves, but three of THE WITCHES OF KARRES!

Synopsis from Open Library.