It's exam time at Xavier's Institute, and young mutants Tempus and Triage are barely surviving the Danger Room. Newly teamed up for a solo X-Copter flight exam, they approach Chicago unaware the Sentinels - giant mutant-hunting robots - have attacked the Field Museum of Natural History. When they receive an SOS from the notorious Sabretooth, requesting help for wounded anti-mutant politician Graydon Creed, Triage is all for calling it in. But Tempus sees an oppurtunity to test their healing and time-manipulating powers for real. Whether it's a trap or a chance for peace, the two students face their greatest challenge, and the X-Men's worst enemies.