Hitman AU, I think.
Arthur Ketch is a hitman. He’s a good hitman and he’s never had any qualms about it, no matter how sketchy his clientele tends to be. That it, until he’s ordered to carry out a hit on Sam and Dean Winchester, the sons of his off-and-on partner, Mary.
He could refuse, but then someone else will take up the hit. Now, he’s caught between a rock and a hard place, risking blowing his secret and putting the only people he’s come to consider close to family in danger, or screwing it all up entirely. Of course, that’s before he learns that the Winchesters have secrets of their own.
This is Not a Blog 