Deluge - Anne McCaffrey

InterGal Corporation has long desired to exploit the resource-rich Petaybee. But the planet and its guardians, led by Yana Maddock and Sean Shongili, along with their twin children, Ronan and Murel, have successfully thwarted every attempt by the Corporation to impose its iron-fisted dominion. Until now. With a bold move, InterGal's military arm has dispatched an invading force to subdue the planet once and for all.

While their parents work to foil the assault, Ronan and Murel are captured and sent to a desolate prison world where an old enemy, Dr. Mabo, waits to continue her cruel experiments on the shape-changing siblings. The twins' only hope of escape lies in the uncharted seas of the prison planet. But in the murky depths, something else is waiting. . . .