When Winter Returns (Rosie Winter Mystery #4)
Kathryn Miller Haines

As Rosie searches for the truth behind his identity—and a way to help heal Jayne's broken heart—she faces an unpleasant homecoming of her own. The newspapers are filled with tales of saboteurs infiltrating the East Coast. Her ex, Jack Castlegate, is also back in Manhattan, nursing severe war injuries, under scrutiny for desertion, and engaged to a gorgeous WAC private. Rosie and Jayne's friend Al is in hiding and no one seems willing to help him out.
Desperate to make things right, Rosie finds herself telling lie after lie to protect her friends and herself. But as her deceit mounts and lures danger out of hiding, she starts to wonder if they weren't all safer on the warfront than they are on the home front.