Adopted to different families shortly after birth, identical twin brothers Scott and Henry grow to manhood having no idea that the other exists. They ultimately wind up on opposite sides of the fence, for Scott "Zipper" Conlon is a member of the Skuldmen, an outlaw motorcycle club, and Henry Baker is a federal law enforcement officer.

During a stakeout, when FBI agent Mitchell Gates observes Zipper leaving the apartment of a suspected terrorist, he implores his old Army buddy to learn what he can about the man. Although uncomfortable doing so, Zipper feels obligated, not only as an American, but because Gates saved his life during the first Gulf War. Due to the Skuldmen's anti-law enforcement beliefs, they agree that their cooperation be kept secret.

A terrorist plot to kill thousands, combined with a woman's revelation that Zipper is Henry Baker the cop, sets off a chain reaction that will shake the Skuldmen to the core, as the brothers react. In an unpredictable story of suspense, murder and mistaken identity, three tales merge into one during the biggest biker party of the year, when All Roads Lead to Sturgis.