 When Piper accidentally messes with the demon of Strife, his colleagues of Death, Famine and War, who are on a deadline to cause the Apocalpyse or be vanquished by the Source of evil and replaced as the Four Riders of the Apocalyps, decide to entrap her, but in the ensuing duel of magic against the Charmed trio, clashing vanquishing spells make both Prue and War disappear into a vortex. The remaining three Riders find themselves forced to cooperate with each-other to get them both back by a reenacting in reverse, while fearing the other side will cheat or strike out once reunited... Leo warns them the risk is too great and then finds the remaining Riders  headquarters in evil action and their identity - should the sisters now abandon Prue or risk causing the End of the world at the millennium (correcting for errors in human chronology)?