January 1977, Utah State Prison. Double-murderer Gary Gilmore is about to become the first convicted killer in a decade to be executed on U.S. soil. Awaiting his fate on death row, Gilmore agrees to a 'one-time only' visit from Mikal, the younger brother he barely remembers. Piecing together fragments of their shared past - born of a brutal father, raised in a family haunted by death, religion and superstition - Mikal searches for a reason to appeal against the execution or to accept that the moment of blood atonement has arrived. Meanwhile, the killer's twisted celebrity, fuelled by a media frenzy, has the eyes of the world looking on.