THE KICKOFF TO THE EPIC TELEVISON CROSSOVER EVENT, CRISIS ON INFINITE EARTHS  – The Monitor (guest star LaMonica Garrett) sends Harbinger (guest star Audrey Marie Anderson) to gather the worlds’ greatest heroes – Supergirl (Melissa Benoist), The Flash (guest star Grant Gustin), Green Arrow (guest star Stephen Amell), Batwoman (guest star Ruby Rose), White Canary (guest star Caity Lotz), The Atom (guest star Brandon Routh) and Superman (guest star Tyler Hoechlin) – in preparation for the impending Crisis.  With their worlds in imminent danger, the superheroes suit up for battle while J’onn (David Harewood) and Alex (Chyler Leigh) recruit Lena (Katie McGrath) to help them find a way to save the people of Earth-38. Jesse Warn directed the episode with story by Robert Rovner & Marc Guggenheim and teleplay by Derek Simon & Jay Faerber (#509). Original airdate 12/8/2019