Dead or Alive — Patricia Wentworth

Meg leaned forward suddenly. There was a note of terror in her voice. "Bill--where--is--Robin?" Robin O'Hara never deserved his wife, Meg. He was unfaithful and involved in work that was just a little bit dangerous. When Meg reaches her limits and wants a divorce, Robin abruptly disappears and is presumed dead. Shortly after, Meg starts receiving messages that gives her the idea that reports of Robin's death may be premature. When former beau, Bill Coverdale, comes back to London he is intent on winning Meg back. He just has to deal with foreboding about her missing husband, a crazy group of kidnappers, and saving her from a watery grave...