Tonight’s episode of Supergirl launches the first salvo in a four-show, two-day crossover story linking all four CW superhero action series from the DC Comics universe. The overall story is called “Crisis on Earth-X,” and it has heroes from the TV universe of DC adventures meeting up with counterparts from an alternate, twisted-mirror universe – kind of like the one several iterations of Star Trek would visit from time to time, where doppelgangers were, by and large, evil and sinister. On Supergirl, that means a version of Supergirl, played by Melissa Benoist, who’s darker in both attitude and wardrobe (pictured). And it means continuing to follow that interdimensional skirmish tonight at 9 ET on Arrow, with part three of the story televised Tuesday night at 8 ET on The Flash, and the conclusion televised Tuesday at 9 ET on DC’s Legends of Tomorrow.