A powerful alien threat arrives on Earth under mysterious circumstances and Barry, Iris and the rest of Team Flash are pushed to their limits in a desperate battle to save the world. But with time running out, and the fate of humanity at stake, Flash and his companions will also need to enlist the help of some old friends if the forces of good are to prevail.

Barry meets Black Lightning at the Hall of Justice after things take a dire turn with Despero. Iris suspects something is off with Despero's vision of the future so she seeks help from a powerful ally.