Legends Mate by Jennifer W. Smith

Scorned siren, Luna, seeks to heal her broken heart on the mystical Wiccan Haus Island, but she doesn’t have a reservation. So, she sneaks onto the island, hoping they’ll let her stay and rent a room. But there has been an assassination threat against one of the Wiccan Haus owners, and Luna’s unscheduled arrival makes her a prime suspect.
Nate, a Sasquatch working for the Para-Elite Force, has come to the private island undercover, posing as a guest. He must flush out the assassin. When he’s assigned to trail the hauntingly beautiful siren, everything goes sideways, and Nate is shaken to his core with yearning and desire. His soul mate could be the assassin, and he may have to choose between duty and love.