Justice League of America, Vol. 1

Criminals from Earth Two have crossed the dimensional barrier into Earth One. Comparing notes with local riff raff, they develop a dangerous scheme. The criminals perform daring crimes on their own Earths, eluding those who fight for justice, and then vanish onto the other Earth to enjoy their ill gotten gains without interference from the law. Unable to sit idly by, they challenge the resident super teams on each world to combat. Seemingly defeated, the Justice League manages to get a message across the dimensional barrier to the Justice Society, bringing them across to Earth One. The two teams then form a new plan, and regroup for a counter attack. The first official Crisis continues in the next issue.