Crisis on Infinite Earths: Part One

The episode is the first part of the five-part crossover, ​.

Synopsis
The Monitor sends Harbinger to gather the worlds’ greatest heroes - Supergirl, the Flash, Green Arrow, Batwoman, White Canary, the Atom and Superman - in preparation for the impending Crisis. With their worlds in imminent danger, the superheroes suit up for battle while J'onn and Alex recruit Lena to help them find a way to save the people of Earth-38.

Trivia

 * Alan Ritchson and Curran Walters reprised their respective roles from the Titans TV series in an uncredited role.

Production
Shooting for began on September 24, 2019.