The X-Men and the Fantastic Four team up in this heart-pounding adventure! Can the two teams put their differences aside to stop a creeping menace from outer space that threatens our planet's very existence? Even as the heroes trek into the stars, the real threat to their mission might just be among themselves! It's the X-Men and Fantastic Four versus...the X-Men and Fantastic Four?! An unexpected adversary turns Marvel's two greatest hero families against one another. Collects X-Men/Fantastic Four #1-5.