Flash of Two Worlds!

Barry Allen vibrates at precisely the right frequency during a stage performance and slips through dimensional barriers onto a parallel Earth -- one where the original Flash, Jay Garrick, is a real person who recently retired. The two speedsters team up to stop Jay's old enemies the Thinker, the Shade, and the Fiddler from ransacking Keystone City. Written by Gardner Fox and drawn by Carmine Infantino -- both veterans of the Golden Age Flash -- the story introduced DC's concept of parallel Earths, naming them Earth-One and Earth-Two. The framework shaped the company's continuity for the next two decades.