Bart Simms was once a young adolescent that met another version of himself that called himself Doctor Tomorrow. He requests his aid in helping to stop a man named Hadrian. Hadrian is trying to reshape the multiverse by eliminating trillions of people.
He soon realizes that Doctor Tomorrow was also trying to do the same. Doctor Tomorrow mistakenly transported Bart into a different reality where he met an older version of his friend, Gretchen.
Gretchen helps train Bart into becoming a hero. When Bart believed he was ready, he soon returns to his reality at the exact time Bart left, in which he fought and defeated his doppelganger.