Darin and Jack MacNamara used half-magic, half–medieval technological bracelets forged by ancient alchemist sorcerers to help enslave demons and force them to fight to the death at their fight club. Anyone wearing the bracelet was confined to an area designated by a red line. Crossing the line meant instant death. Wesley Wyndam-Pryce and Cordelia Chase determined that could be unlocked using strands of horsehair.