If you're new to the Karen Vail series, this may be a good place to start, although this is not the first book. The story toggles back and forth between the present and the first appearance of the serial killer during Karen's rookie year when she worked the homicide with her mentor Russo. The story also follows the Greek family who were affected by the killing spree.
Although the story moves back and forth between the present and Karen's earlier career, it's easy to follow. I did feel that the inclusion of the extensive chapters on the Greek family slowed the pace, but they were interesting and relevant. At the end, the pace picks up and it's hard to put the book down before the resolution.
If you enjoy police procedurals, particularly ones with a female protagonist, this is a novel you'll enjoy. Karen and Roberto come across as real people. The plot is strong, and the ending is full of action.
I reviewed this book for Net Galley.