11 - Door Through Space by Marion Zimmer Bradley

Once hailed as the top Terran Intelligence agent on the enigmatic planet of Wolf, Race Cargill has faced death countless times among the planets strange half-human and non-human inhabitants. His daring missions brought him fame and glory, but all that changed six long years ago. Now confined to a mundane desk job at Terran Headquarters, Cargills life has become a monotonous routine, a far cry from his thrilling past. However, when THE DOOR THROUGH SPACE unexpectedly swings open, old rivalries reignite, and a dangerous plot threatens the very foundation of the Terran Empire.