Comics legend John Byrne bridges the gap between the X-Men's classic and all-new, all-different eras! In this series, skillfully woven between the X-Men's 1970 cancellation and 1975 revival, thrill to previously unknown exploits of the strangest teens of all as they search the Savage Land for Magneto! Iceman goes it alone; tragedy strikes Angel; and Beast, Cyclops and Marvel Girl encounter a young mutant named Ororo! The X-Men head into space with the Fantastic Four, Sauron soars again, the Brotherhood of Evil Mutants returns, and the team faces the mysterious group the Promise! Plus- Sentinels, Kraven the Hunter, the Mole Man and the Yeti! And it all concludes with a seamless "crossover" with a classic FANTASTIC FOUR tale! Collecting X-MEN- THE HIDDEN YEARS #1-22, FANTASTIC FOUR (1961) #102-104, and material from X-MEN (1991) #94 and AMAZING ADULT FANTASY #14.
— Description from Comic Vine community (comicvine.gamespot.com).
