Both Ends of the Night (Sharon McCone Series)

Sharon McCone's flight instructor Matty confides that her boyfriend, John Seabrook, is missing and asks McCone to find him. Shortly afterwards, Matty is killed in an "accidental" plane crash. Sharon discovers that, a decade ago, Seabrook was placed in the Federal Witness Protection Program after testifying against a man who has been missing for the last ten years. Following sinister leads, Sharon travels to a frozen wilderness - and comes faces to face with Matty's killer.