His Challenger (The Lone Family #3)
Ace Fawn

All Rex needs to do is make sure Mathew doesn’t escape. But Mathew fights back and proves he is a force to be reckoned with. Rex is consumed by a strong desire to dominate Mathew and to make the enemy his own. Rex must stay in control, but the longer he and Mathew are alone together, the harder it is for Rex to resist the sexy assassin.
Dangerous men, especially killers, are not supposed to love each other. Mathew knows he shouldn’t be attracted to the enemy, but he develops a hunger for his captor that he hasn’t experienced before … and Mathew can’t deny himself any longer.
Trigger Warning: This book contains explicit sexual content, spanking, age-gap relationships, kidnapping, dubious consent, self-harm/attempted suicide, and violence. Reader discretion is advised.