Lethal Hearts. Mafia Lords, #4

Harper Valenti doesn't have a choice. Reduced to a pawn in a sick Don's game, Harper is tasked with seducing and killing Bratva Pakhan Mikhail Konstantin. Failure means her father's death and her own, but even the best-laid plans tend to unravel. Harper finds herself on the receiving end of a cold and calculating crime boss but Mikhail isn't what he seems. Most men would immediately dispose of their assassins but Mikhail Konstantin is unlike most men.
Harper doesn't just intrigue him. She's become his new obsession. It doesn't hurt the sparks between them burn undeniably hot. Mikhail decides to take care of his problems in one fell swoop. He'll take care of their common enemy. In return, Harper will be his wife and Mikhail will make sure the ties that bind them will never be broken.