After years of searching, Rex's older brother, Titanium Dax, becomes the second Subtopian ever to find his way to the earth's surface. He and his rock monster slave, Liplor, are thrilled to find that Rex is alive and well, but their reunion is soured when Dax threatens to reveal a dangerous secret about Rex's origins.

The Subtopian army has come to the earth's surface, and their enslavement of the human race has begun. The League of Freedom must join forces with the villains of The Injustice Club in order to stand a chance against the Subtopian invasion, but Rex, Lex, and Dr. Devizo cannot set aside their differences.