Warning: SPOILERS for Extermination #1.

The latest X-Men event has kicked off with a major death. The All-New X-Men's presence in the present day is warping the timeline to disastrous effect, and the famed time-traveler Cable has arrived from the future to put matters right. He clearly doesn't care who dies in order for him to achieve his mission... including himself.

In 2012, Brian Bendis launched a fascinating story in which Beast pulled the original X-Men out of their own timeline, and into the present. Since then, the Original Five have struggled to deal with the reality of the world they will help to build. It's been particularly hard for Cyclops and Jean Grey, who learned of a future in which one was believed to have committed genocide, and the other was blamed for the destruction of entire worlds. They've recently learned that the original X-Men must return to their own time in order to secure the fate of the timeline, but the teenagers are understandably reluctant to do so; they know their memories will somehow be erased, they'll lose every lesson they've learned from this experience, and their fates will be sealed.

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All that's come to a head in this week's Extermination #1, an event miniseries that sees a time-traveler emerge from the future, determined to force them to go home. He's swiftly opposed by another time-traveler, Cable - and things don't go well for Nathan Dayspring Summers. Cable is gunned down down, his death causing a psychic shockwave that alerts the X-Men to what's going on. They rush to his side, the different X-Men teams united in grief at the loss of one of their own. It's particularly painful for the freshly-resurrected Jean Grey, who has barely had the chance to spend any time with her son before she looked down at his cooling body.

But time-travel is complicated. There appear to be two dangerous factions at work here, not just one. The first - who targeted the All-New X-Men earlier in the issue - is Ahab, a mutant hunter from the "Days of Future Past" timeline. The murder has been committed by the second, though, and his identity is a wonderful twist. The issue closes with the revelation that Cable's killer is actually a younger version of Cable himself. Little wonder the murderer stood over his fallen future self and snarkily observed, "Old fool, you really should have seen that coming."

The X-Men comics have always delighted in using time-travel as a major plot device; it's the driving concept behind important arcs like "Days of Future Past," "Age of Apocalypse," "X-Cutioner's Song," and "Battle of the Atom." It seems this latest event, "Extermination," is destined to explore the same kind of ideas - but in fresh and exciting ways. There's a heartbreaking sense of finality to the idea that Cable could only be killed by Cable. What's more, given the event's ominous title, it's likely Cable will only be the first casualty.

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Extermination #1 is on sale now from Marvel Comics.