Cain killed Abel: the original murder. But the Bible is silent about one key detail: the weapon Cain used to kill his brother. It's a mystery that's never been solved. Until now. In Florida, Cal Harper comes face-to-face with his family's greatest secret: his long-lost father, who's been shot with a gun that traces back to an unsolved murder in 1932. What could that murder have to do with the biblical one? Father and son are suddenly thrown into a bloodthirsty quest for an ancient weapon, and the answer to a secret that people are dying to find. But closing in on them is a man tattooed with the mark of Cain - the world's first killer. In his pocket he carries the means of causing a horrifying death. And in his heart an insatiable desire for what he believes is his birthright . . .