Violet

From publisher blurb: In this installment: If there is a name that causes a shudder to go through the underworld, and worry even the hardest of mooks, that name is VIOLET. She's only been in the business a handful of years, but she's left behind her a trail of bodies and broken souls. Around her, people die silently, or choking on their own blood, or just taken away screaming. She is the most methodical assassin on the market -- an expert in poisons who the bosses always want to keep busy. Because if she isn't occupied with one task or another, she might get bored -- and everyone is terrified of what will happen then.