The Fenaday and Shasti Chronicles Series by Edward McKeown, Janet E. Morris

A rag-tag crew of spacefarers become unexpected heros battling an ancient enemy on a murdered world. Reluctant privateer, Robert Fenaday searches the stars for his lost love. He's joined by the genetically engineered assassin, Shasti Rainhell, whose cold perfection masks a dark past. Both are blackmailed by government spymaster, Mandela, into a suicidal mission to a doomed planet... moreA rag-tag crew of spacefarers become unexpected heros battling an ancient enemy on a murdered world. Reluctant privateer, Robert Fenaday searches the stars for his lost love. He's joined by the genetically engineered assassin, Shasti Rainhell, whose cold perfection masks a dark past. Both are blackmailed by government spymaster, Mandela, into a suicidal mission to a doomed planet. Leading a team of scientists and soldiers, they must unravel the mystery of a world's death, before an ancient force reaches out to claim their lives. less

"Having survived the nightmare world of Enshar, Robert Fenaday abandons privateering and his quest for his lost wife to begin life anew with the genetically engineered assassin, Shasti Rainhell. But spymaster Mandela has other plans for the pair, intrigue and murder on Shasti’s home planet of Olympia. Fenaday must fight his way to Shasti, facing her deadly creator and an alien mystery that could destroy the Confederacy."

Robert Fenaday must drive the starship Sidhe across uncharted space to rescue his wife before war breaks out. But can he keep his command from mutiny and his former lover Shasti Rainhell from murder as well?