Darkening Skye by Adalind White

The Big Apple is not supposed to bite back.

A middle aged New York cop goes undercover as the father his much younger colleague to catch a serial killer who preys on young female tourists.
At the end of their assignment, they have to deal with their feelings in the real world. How will reality measure up to the fantasy?
Homicide Detective Nicholas Woods gets bad guys off the street due to his startling insight into the twisted minds of killers. For the past ten years, his partner, Katherine, was his only anchor out of the darkness. She is the person he trusts most in the world, but his Captain sends him on the trail of the Tourist Murderer without her. What’s worse, he’s saddled with a detective two decades his junior who has limited field experience. Woods never liked the fresh-faced college girl next door type, but he never had to live with one before.

Being professional was never as hard as when she calls him Daddy.
Tall, blonde and California tanned, Skye was a happy cop until she got shot on duty during her first deep cover mission. She finds herself transferred across the country, and relegated to a desk job where the highlight of her days is to devour the archived cases of the legendary Nicholas Woods. When she gets partnered with her idol because she can look the part of his daughter, hero worship turns into something unexpected. The bubbly vanilla girl discovers a new side of herself. Skye finds herself sliding into a darkness she had never acknowledged.