At the X-Mansion, Beast investigates the biological origins of the powerful enemy they have just captured, while also revealing the possibility of mankind's genetic extinction within the next few generations.

This story also led to the introduction of Cassandra Nova (Professor Xavier's previously unseen twin sister, who escaped from the womb via miscarriage after the two siblings engaged in psychic combat against each other).

The term refers to mutants who possess multiple powers, a longstanding tradition of the X-Men books that had never been officially addressed by writers.

The concept was mainly incorporated by Morrison to provide Emma Frost new diamond skin powers, allowing her to serve as a replacement for the recently deceased Colossus.

The initial paperback did not have "New X-Men Annual 2001", which was omitted due to issues involving how to reprint the story, which was published in the sideways "Widescreen" format.