They are the next link in the evolutionary chain - a new breed of superhero. Each was born with a unique genetic mutation, which manifested itself in extraordinary powers. In a world increasingly filled with hatred and prejudice, they are outcasts who are feared and loathed by those who cannot accept their differences. Yet they fight to protect a world that fears them. In X2:X-Men United, the next adventure in the X-Men saga, the X-Men face their most dangerous mission ever, and must stand united with their enemies to combat a menace that threatens mankind - and mutantkind.