The Galactic Whirlpool

Summary
From the back cover: Beyond the realm of the Federation, beyond the edge of the galaxy, a lost colony of humans in space drifts inexorably toward the galactic whirlpool. Kirk blazes new star trails to these strange people, isolated for centuries. Unless he can convince them that the Enterprise crew members are not "demons," they will be sucked into a churning one-way funnel of doom!