Iryal and McKayla Asha are not normal. They were raised by their uncle and trained at a highly secret academy in the northern mountains of Scotland. One became a deadly, highly skilled, and talented assassin. The other became a gifted alchemist. Together, they form one of the most formidible teams within the whole of the Assassins.

Dean and Sam Winchester have been hunting monsters for as long as either can remember. After finding a Men of Letters bunker, they surreptitiously become members. The bunker holds a treasure trove of knowledge, including a scant amount on the Assassins.

Little do they know that their two worlds are about to collide, in a very big way.