Ruthless by Cheyenne McCray

Alexi Steele is determined, relentless, and driven to protect the innocent. She’s a top agent of the NSA’s covert Recovery Enforcement Division, specializing in human trafficking and sex crimes. Her current assignment: Infiltrate the inner circle of Boston’s exclusive S&M clubs to save young women who are days away from being auctioned off to the highest bidders. But Lexi’s only way in is under the control of her new partner, Nick Donovan.
Nick will do whatever it takes to bring down the billionaire, sex-ring mastermind who’s kidnapped his sister. But the games he must play as Lexi’s dominant are burning away his icy control and blurring the lines between work and desire. Meanwhile, their enemies are close to discovering their true identities, and a devastating race against time brings them dangerously close to a ruthless end.