King Slayer by Layla Reyne

Never fall for a mark. Mission fail.

Christopher Perri—a.k.a. Dante Perry—infiltrated the Madigan organization with one goal: vengeance for his murdered partner. Falling for the assassin at the head of the table wasn’t part of the plan, but Hawes Madigan is not the cold, untouchable Prince of Killers Chris expected. Everything about the newly crowned king is hot, and every inch of him eminently touchable… and off-limits once Chris’s cover is blown.
Exposure couldn’t come at a worse time. Hawes’s throne is threatened, and Chris suspects the same person who killed his partner is behind the coup. Working with Hawes benefits them both, but Chris’s employer has other ideas. Dismantling criminal organizations is what Chris does best, and his boss expects the King Slayer to deliver.
But Hawes is taking the Madigans in a new direction, one Chris can get behind, and the two men form a shaky alliance strengthened by the irresistible attraction between them… until Chris learns who killed his partner. Once he knows the truth, the King Slayer is unleashed, and Chris will stop at nothing to destroy those who betrayed him, including the king who stole his heart.