The Ultra Big Sleep — Patrick Swenson

Dave Crowell is a hero of the eight worlds of the Union, but he doesn't want fame or fortune. These days he just wants to run his private detective business with his partner and forget about the Ultras, the insidious aliens that attacked the Union, then vanished. But a client turns up dead under mysterious circumstances, and Crowell knows the Ultras have not gone away. With the help of a beautiful alien, he uncovers fragments of memory that might lead to his missing father. When it becomes clear that Crowell's past also contains the information he needs to save the Union, he is caught up in a conspiracy beyond his understanding and pulled into an underworld drug war on a hostile planet. With the crisis deepening, Crowell must learn the answer to the biggest question of all: Where are the Ultras?