When it becomes clear that the presence in the current dayof the original X-Men is endangering the whole of existence, Beast is ready to send them back. Faced with the horror of what awaits them, however, the young Jean Grey and Scott Summers are determined to remain. The ensuing, highly emotional, debate is disrupted by the arrival of yet another team of X-Men; they are from the future and bear a warning not to make history's greatest mistake.