Callahan and Caleb Matthews are reunited in Denver to follow up on a kidnapping case that Siobhan was working on. This unexpected reunion catches both of them by surprise. It had been over a year since they last worked together. And feelings that had simmered below the surface all that time might be reignited. But does either of them really want that? Or is this just a chance to solve another case with international overtones. Murder, kidnapping, and a mysterious motive take them on a ride like no other. Will they survive? Will their friendship survive? Will they discover the FOUNTAIN OF YOUTH?