Ultimate X-Men Vol. 9: The Tempest
Brian K. Vaughan (Writer), Brandon Peterson (Artist)
Bound together by their unique genetic heritage, the mutant members of the X-Men have become more than just a team - they've become a family. But even the strongest family can be ripped apart by tragedy... and the death of one of their own leaves the remaining X-Men struggling to deal with the loss. And even before a moment of silence can pass, the mysterious Mr. Sinister arrives, intent on giving the X-Men a lot more to mourn!
Ultimate X-Men #46-49