Book 2 of 'The Chaos Engine' trilogy.
One week: That was all the time given to the X-Men to correct a universe threatening flaw after Roma, Supreme Guardian of the Omniverse, discovered that unknown forces had severely altered the structure of the heroes' home dimension.
It hadn't taken them long to track down the source of the disruption: the tyrannical Doctor Doom, in possession of the Cosmic Cube - a device that allows its owner to twist reality and create their personal vision of a perfect world. They X Men failed in their mission, though, and now the Cosmic Cube is in the hands of their longtime enemy, Magneto, the Master of Magnetism.
Magneto has a dream that one day Homo Superior will freely walk the Earth as masters of the human race. Now that day has come, and the only hope the world has to survive is in the hands of Doctor Doom and the one X-Man not affected by the reality-changing powers of the Cube. But unknown to any of the players in this cosmic chess match, there is one final participant waiting in the wings . . .