When aliens called the Dominators attack Central City, Barry speeds over to Star City to ask the Green Arrow for help in stopping them. Realizing the battle against the Dominators is bigger than they thought, they track down the Legends of Tomorrow, and Barry and Cisco create a breach to bring back a secret weapon – Supergirl. Once all of the super friends are assembled, they come up with a plan to attack but a shocking secret related to Flashpoint is revealed and suddenly no one is sure who they can trust. Meanwhile, Wally wants to join the battle against the aliens but Iris tells him he’s not ready.
The crossover starts on Supergirl S02E08 Medusa (I). It continues on Arrow S05E08 Invasion! (III) and DC's Legends of Tomorrow S02E07 Invasion! (IV).
Quest roles:
Stephen Amell(Oliver Queen / Green Arrow / The Spectre), Melissa Benoist(Kara Danvers / Supergirl), Caity Lotz(Sara Lance / White Canary), Brandon Routh(Ray Palmer), David Ramsey(John Diggle / Spartan), Audrey Marie Anderson(Lyla Michaels / Harbinger), Emily Bett Rickards(Felicity Smoak), Dominic Purcell(Mick Rory / Heat Wave), Victor Garber(Prof. Martin Stein (voice)), Franz Drameh(Jefferson 'Jax' Jackson / Firestorm), Willa Holland(Thea Queen / Speedy), Sonia Beeksma(KPJT Reporter), Christina Brucato(Lily Stein), Jerry Wasserman(President), Donnelly Rhodes(Agent Smith), Linda Ko(NSA Official), Robin Atkin Downes(Dominator (voice))