She's the devil

They ruined her life without knowing. After six years she's back and more powerful than ever. Now everything has changed. She's a serial killer, that always gets what she wants. And she wants revenge. So does he, but little does he know the little girl that plays with poisons is far gone and in her place is a woman more deadly than he could have imagined and she'll do about anything to destroy him. He is as deadly as her, as a boss of the most dangerous mafia in the whole world, that's his job, to kill.
When she comes to ruin them, she never expected to fall in love. When time for the endgame comes how will she end it all?