Teen Titans, Vol. 1

First appearance of Aliens of “Dimension X.” The Teen Titans discover that Hillsdale High actually is the secret base for an alien takeover, and that the school principal is one of the extradimensional alien leaders. Entering “Dimension X,” they rescue Chet and his fellow students from being trapped in the alternate reality and being replaced by duplicates. Kid Flash then uses his vibrational powers to sever the link between the Hillsdale High of Earth and that of Dimension X.