Secret Killer (#Wattys2016)

You thought you were safe. You thought you got rid of her but you didn't, you couldn't. Each victim dies with a scar. On the nape of their neck there is always an H, carved with a century old switchblade. No one knows who she is or where she stays, or how to find her. Then the mission hits to close to "home," or at least what used to be home. But here's the catch.
Mr. Perfect isn't just some helpless Hot Guy, he knows how to kill to.
Uh-oh, you thought it was over, guess again.
He remembers her too.
So who kills who?
Or do they fight the odds to stay together?