During a blackout, Castle and Beckett investigate the death of mental asylum patient Gabriel Shaw, who arrived at Castle's PI office carrying an ax. Shaw, apparently, believed his divine mission was to stop the Antichrist. Castle fears a demonic threat while the team looks into the asylum, a missing orderly, tycoon Victor Crowne, whom Shaw tried to murder as a child, and Oscar von Eckland, heir to another Antichrist-fighter.
—KGF Vissers