In Deep Water by Sam Blake

Second Hand 

Detective Garda Cat Connolly is back at work after the explosion that left her on life support. Struggling to adjust to the physical and mental scars, her workload once again becomes personal when her best friend Sarah Jane Hansen, daughter of a Pulitzer-winning American war correspondent, goes missing. Sarah Jane is a journalism student who was allegedly working on a story that even her father thought was too dangerous. With Sarah Jane's father uncontactable, Cat struggles to find a connection between Sarah Jane's work and her disappearance. But Sarah Jane is not the only one in deep water when Cat comes face to face with a professional killer. In the world of missing persons every second counts, but with the clock ticking, can Cathy find Sarah Jane before it's too late?