Lords Temporal - The Lords of Time - Stan Wychoff never meant to be a spaceman. Still less did he mean to tangle with the powerful Lords Temporal, aliens who hijacked the unlucky Corona as a replacement for their own ruined vessel. With the Corona and its crew under their control, they could continue to ply the timelanes, stealing precious artifacts wherever they dared and selling them to collectors uptime and down. Still, a man who can pass himself off as ship's storekeeper with no prior experience has a few tricks worth knowing. Wyckoff knew there was no chance anyone on the Corona would return to Earth as long as they Lords were in control. So he had to take matters into his own hands.... (from the back cover of the Baen Books first edition)
Source · ISFDB CC BY 4.0