It’s the big Bishop issue, where he joins the team.
It’s basically one long gun fight with Bishop and his allies against the mutants of the future, like Trevor Fitzroy.
I’ve tagged everyone from this time-displaced story because they may (or may not) be 616 canon. Is it a flashback if it takes place in the future? Is it a flash-forward if it is only a possible future?
As a new character, this issue is a helpful way of learning his power set.
Also, in a flash-forward to the future that Bishop comes from, we see a video of Jean Grey–back in our own timeline–warning that there is a traitor among Charles Xavier’s mutants. That traitor kills Xavier.
It’s not clear at what point in time Jean made the recording, and she is murdered before she can name her killer. During the Onslaught event, we learn that the killer is Xavier himself. It’s a HUGE disappointment.
So we’ll be hunting for a traitor in the X-groups’ midst now. It’s going to lead to a bunch of fights between Bishop and Gambit because Gambit, in the future (a future?), is imprisoned by Bishop.
Bishop will be a central character in ’90s X-Men.