Sir Ian McKellan introduces us to the young "Dunstan" (Ben Barnes) who hops over the wall and encounters a young girl, enslaved by an enchanted chain. Neither are slow on the uptake, and into her wagon they go... Nine months later, a package arrives at their door and we meet "Tristan". Many years later, he (now Charlie Cox) proves to be a bit of a chip off the old block, and when told of his progeny decides that he,…