Collects Uncanny X-Men (1963) #129-137. The biggest and best adventures of Marvels mighty mutants — these are the X-Men Milestones! It doesnt get any more iconic than this tale of triumph and tragedy! The X-Men have fought many battles, embarked on galaxy-spanning adventures and defeated enemies of limitless might — but none of it prepared them for the most shocking struggle they would ever face. One of their own, Jean Grey, has gained cosmic power beyond all comprehension — and that power has corrupted her absolutely! Now the X-Men must decide between the life of the friend they cherish...and the possible destruction of the entire universe! This touching tale of ultimate power and the triumph of the human spirit has been a cornerstone of the X-Men mythos for decades. Relive the saga that changed everything!