Seeking to save earth from a menacing but enigmatic alien intelligence, Dr. Warboys and three extraterrestrial comrades set off on a mission that ultimately takes them beyond the limits of the known universe to a distant quasar that serves some unguessable purpose in the intergalactic scheme of things. Somehow the quasar flips the travelers back through space and time to an earth that proves not to be the same planet from which they departed. An old fashioned sense of wonder SF novel, replete with burnished scientific detail, but leaving open more questions than it answers.