A terrible evil invades Sunnydale, setting off a quartet of disasters. Earth, air, fire, and water are each represented on a box moulded from skin and bone. Research leads Buffy and Faith to Kit Bothwell, the watcher of Buffy's predecessor. Together they fight an evil that predates humanity itself.

Buffy tells Giles of her visions of disasters involving earth, air, fire, and water and of a primitive figure holding a box made of human skin and bone. Giles finds the last Slayer to see such a box was Buffy's predecessor, India Cohen. Teaming up with India's Watcher, a sorcerer named Kit Bothwell, Buffy sets off on a history-spanning journey that forces her to confront her own legacy as the sole inheritor of a Slayer continuum.