Ultimate X-Men #99
an issue of Ultimate X-Men by Marvel Comics
Issue description
It's a mutant massacre at Xavier's! In the wake of Ultimatum -- a band of humans have stolen Sentinel technology and attack Xavier's mansion -- killing any mutant they see. With the X-Men locked in battle with Magneto -- can anyone save these students? Their greatest hope might rest in the hands of their worst enemy as the Weapon X program returns!