As the X-Men embark on their inaugural world tour, they must confront some unsettling truths about their mentor, Professor Charles Xavier. Before founding his school for young mutants, Xavier abandoned his son, David, a mutant with uncontrollable reality-warping abilities. Now, David has returned, looking to exact revenge on the father. Ultimate X-Men: Ultimate Collection (Book 2) contains issues 13-25 of the Ultimate X-Men series.