The Challenge Of The Untouchable Aliens! * 1st EARTH-FIFTEEN While in their civilian guises Wonder Woman and Superman visit a flying military fortress, when it suddenly is knocked out of the sky. The two save the crew, but the ships primary weapon is removed and aimed at Central City, but is ultimately stopped by the two with the aid of the Flash. Deciding to solve the mystery behind the cannon, the trio call together the rest of the Justice League, and all agree to aid in figuring out the cause of the strange events. Splitting up into groups they come across a series of stone giants whom are partially intangible, each group collecting devices that threaten to destroy various cities on Earth. These beings actually come from an alternate universe comprised of anti-matter which is slowly losing its vibrational sync causing it to merge with the Justice Leagues Earth, the result would cause the destruction of both worlds. The Stone giants were hoping to destroy the cities on the JLA's Earth, when merged with their own world's cities. When the creatures were able to will the Green Lantern's power ring out of his hands due to their supreme will power, they played into the Lantern's trap, allowing the JLA to follow the stone creatures to their own reality. Realizing the truth of the situation, and that any attempt to move the giants cities would cause a powerful nuclear explosion (caused by bombs placed in the buildings that would be used against any invaders) the JLA instead work together with the giants to prevent their worlds from merging, with Green Lantern restoring the vibrational barrier between worlds with his power ring.