Orion Arm - Julian May

After a brief (but heroic) fling with all that is right and just, Asahel Frost has reverted to his true nature—undisciplined and feckless, according to the girlfriend who just dumped him. Now he is once again the legal nonentity known as Helmut Icicle, living the riverboat skipper life in a tiny galactic outpost with the rest of the ne'er-do-wells.
That is until his sister Eve, herself genetically altered by the alien Haluk, begs Helmut to expose the Haluk's conspiracy, which threatens humans throughout the Spur worlds. Genetic alteration is tightly controlled, yet now it's running rampant. Helmut must find the culprits, but time is running out. Too many people have vanished into the secret empire where an evil genius reigns supreme. Worse yet, there's an unknown traitor in Helmut's own family who is quite willing to murder. Only one thing's clear: Helmut will emerge either triumphant . . . or dead.