Snapshot

The award-winning author's Boston PI returns in a mystery "destined to secure Barnes' position in the hotshot ranks of detective fiction" (Arizona Republic).
Six-foot-tall, redheaded ex-cop and Boston-based private eye Carlotta Carlyle is "the genuine article: a straightforward, funny, thoroughly American mystery heroine" (New York Post).
Carlotta Carlyle is sorting through her junk mail when she finds a snapshot of a newborn baby she has never seen before. One week later, another arrives showing the same child one year older. The next week, a third arrives. As the deliveries continue, Carlotta becomes obsessed with this unnamed little girl and is drawn into one of the most dangerous assignments of her career.

The girl was named Rebecca and she died of leukemia at the age of seven. Her grief-stricken mother has never been able to accept what happened, so she hires Carlotta to investigate the highly regarded hospital where someone on staff seems to have forgotten the most important lesson of a doctor's training: Do no harm.
Snapshot is the 5th book in the Carlotta Carlyle Mysteries, but you may enjoy reading the series in any order.