Dead Drift by Dani Pettrey
Seven years ago, operative Luke Gallagher vanished to become part of an elite team set on capturing a deadly terrorist. When Luke returns to face those he left behind, their help becomes his only hope of stopping his target's latest threat of an attack that would shake America to its core.
Private investigator Kate Maxwell never stopped loving or looking for Luke after he disappeared. But she also never imagined he left her or his life by choice. Now he's back, and together they must unravel a twisting thread of secrets, lies, and betrayal, all while on the brink of a biological disaster.
Will they and their love survive, or will Luke and Kate become the terrorist's next mark?