Cisco and Chester travel back in time and get stuck in 1998, repeating the same day over and over again. The key to returning home is at Chester's childhood home but he refuses to visit.

When Ultraviolet returns to Central City, Allegra is determined to find her cousin and change her heart. Meanwhile, Joe finds evidence that Kristen Kramer may not be the good cop she appears to be.

John Diggle arrives in Central City with a weapon to help Barry stop the Godspeed War. Meanwhile, Allegra and Ultraviolet's new bond is put to the ultimate test, while Joe and Kristen Kramer are hunted by a former colleague of hers.

The Flash enlists a host of speedster allies, including Iris and his children from the future - Bart and Nora West-Allen - to end the speedster war and defeat a deadly new adversary: the villainous Godspeed.

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.

Barry trusts his instincts during a murder investigation, believing the suspect, despite the overwhelming evidence against him, meanwhile Iris gives Allegra an opportunity to be a mentor.

Barry's desire to keep Team Flash safe is tested when Frost recklessly courts danger as she tries to stop the "Black Flame," meanwhile, Iris tries to help a teen girl reunite with her mother but unintentionally does more harm than good.