Writer/artist John Byrne's retro take on the X-Men - set between their Silver Age series and their All-New, All-Different incarnation - comes to a calamitous conclusion! The original X-Men take on the Brotherhood of Evil Mutants, mutant-controlled Sentinels, Angel's evil uncle Burt, the long-lost Yeti, Kraven the Hunter and the mysterious mutant group the Promise - and it all concludes in a seamless 'crossover' with a classic Lee/Kirby/Romita FANTASTIC FOUR tale! Plus: The original version of that FF saga, featuring the menace of Magneto and the Sub-Mariner! And the classic Atlas Era and Silver Age appearances of the Promise! Collecting X-MEN: THE HIDDEN YEARS #13-22, FANTASTIC FOUR (1961) #102-104, and material from YELLOW CLAW #2 and AMAZING ADULT FANTASY #14.