The Kystrom Chronicles

When linguist and smuggler Sean Wren is blackmailed into a job to get some data off an ancient ship, he's not expecting it to be the Philosopher's Stone: a literal recipe for immortality. Unfortunately, he's not the only one looking. The undying Ministers, mysterious aliens that have ruled over humanity for thousands of years, want the data too. So does the Republic, the last free human government. To add to the fun, the map to the treasure is in a long-lost language, the ship's filled with dangerous traps and genetically engineered monsters.

Having escaped the dangers of the Nameless with the Philosopher Stone data, Sean thought his troubles were over. Until he gets a call for help from his sister Brigid—his long-dead sister. Brigid is sparse on the details, but she needs Sean to go to the Republican city of Illin to retrieve something called a "Purifier" for her. Reeling from the desperate hope that his sister is alive, Sean aims for Illin, dragging his new companions, Tamara, formerly a Republican soldier, and Indigo, the Minister responsible for the destruction of Sean's home, into the fray.