The CW’s superheroes—The Flash, Green Arrow, the Legends of Tomorrow and the rest of the crime-fighting residents of Star and Central Cities—have fought off many a Big Bad from their Earth (and Earth-2). But this time, the threat is extraterrestrial—which is why they call in their friend Supergirl to help in 2016’s big DC TV crossover event.

The villains are an alien race called the Dominators, and they’ll wind up on Earth (well, Earth-1) because of something to do with the metahumans. The storyline is based on the DC Comics crossover Invasion, and executive producer Marc Guggenheim says the idea for this year’s event was based on an idea from DC TV super-producer Greg Berlanti.
E Online