When a powerful alien threat arrives on Earth under mysterious circumstances, 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.

After returning home from a visit for their parent's vow renewal, Bart and Nora quickly realize that things are not exactly as they left them. The duo race to repair any fissures in the timeline and restore everything back to the way it is supposed to be.

The Flash and team are in for the fight of their lives, meanwhile, Iris discovers the cause of her time sickness.

With The Flash still reeling from everything that just happened, the rest of the team rallies to support him when he needs it the most.