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.

Barry and Iris greet their future children, XS and Bart, only for a shocking secret to threaten their new familial harmony. Meanwhile, the Godspeed war intensifies and threatens to destroy Central City.

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.

The Flash, the fastest man alive, is tasked with his greatest challenge yet, to save the timeline and save existence. Friends old and new gather for an epic battle to save Central City, one last time.