Was Once a Hero: Book One of the Fenaday and Shasti Chronicles

Reluctant privateer Robert Fenaday searches the stars for his lost wife. He's joined by the genetically engineered assassin Shasti Rainhell, whose cold perfection masks a dark past. Government spymaster Mandela blackmails them both 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.