Surrender to Sanctuary. The Sanctuary Trilogy, #1

HOW FAR WOULD YOU GO?A young woman is brutally murdered, her body dropped into the sea and carried by the tides onto the beach at a federal park at the Jersey Shore. Hometown investigators believe the woman simply partied too hard and fell overboard, but FBI Agents David Owens and Anna Parker know better. David and Anna quickly trace the victim's path from a local adult BDSM club to a dangerous and shadowed world that caters to those who practice a lifestyle of domination and submission, and not just for fun and games.
To find the truth and stop a madman before he can kill again, they will need to break all the rules. They will need to pose as Master, and as slave. And despite their growing attraction and possibly love for each other, they'll need to give the performances of their lives - because discovery means certain death.