In the Shadow of Evil by Nancy C. Weeks

Elías Mendoza’s personal vendetta against the McKenzie family rests on Jennie’s shoulders. As she cradles the bullet ridden body of her ten-year old student, she knows Mendoza is responsible. Quinton’s death is a message. Jennie’s life belongs to only Mendoza. But she has her own message. No one else dies. Her life means nothing as long as Mendoza is free.
Jared McNeil has spent ten years with Maryland’s Special Crime Unit and very little rattles him. When the haunted teenager he once tried to protect walks into his precinct now a beautiful woman, he wants nothing more than to wrap her in his arms and never let her go. But she’s there to settle her debts before she goes after his nemesis, Mendoza. Jared’s vow to stay away from Jennie until the task force destroys Mendoza now means nothing.
There are forces at play greater than the evil shadowing them, but time is running out. United, they can do anything. Alone, they will fail.