In a bleak future where Sentinels have all but exterminated mutantkind, the X-Men's last survivors send Wolverine's consciousness back into his younger self to stop the assassination that started it all, Mystique's killing of weapons designer Bolivar Trask in 1973. Reuniting a fractured young Charles Xavier and Erik Lensherr is the only way to change history, but Wolverine has only days to pull it off before the future he remembers closes in for good.
Summary by Loreful, from public sources