Crisis on Infinite Earths?

"Who exactly are you, and why are you stopping me?" At that moment, Barry's expression turned extremely grave. The sudden disappearance of a universe that had once existed reminded him of a crisis he had only recently learned about, one that was about to sweep across the entire universe. So right now, he had to hurry to the universe he knew best, find powerful allies, and stop this crisis. "Who I am isn't important. What matters is whether you know the real reason this universe disappeared.