Apocalypse's long-prophesied ascension begins! As Professor X grows paranoid and withdrawn, the X-Men split up - leaving only a small team to aid a friend. And when Apocalypse's newest Horseman of Death strikes, an X-Man will perish! But not everything is as it seems - and as the team realizes the full scope of Apocalypse's scheme, it may be too late! Only the Twelve, a gathering of mutants foretold to save the world, might turn the tide - but Apocalypse plans to use them to become a god! Who will make the ultimate sacrifice to prevent the Ages of Apocalypse from becoming a horrifying reality? Collecting UNCANNY X-MEN (1981) #371-380 and ANNUAL '99; X-MEN (1991) #91-93, #94 (A STORY), #95-99 and ANNUAL '99; X-MEN UNLIMITED (1993) #24 (A STORY) and #25-26; GAMBIT (1999) #8-9; ASTONISHING X-MEN (1999) #1-3; WOLVERINE (1988) #145-149; CABLE (1993) #71-78; X-MAN #59-60; X-51 #8; X-FORCE (1991) #101; and X-MEN 1999 YEARBOOK.