【[Ep4] Secret Campus】

Stop me if you've heard this one: 10 superheroes walk into a warehouse... To find out what happens next,[Ep4] Secret Campus you'll have to tune in to The CW's epic crossover event, which brings together heroes from Supergirl, The Flash, Arrowand DC's Legends of Tomorrow to face off with an alien race known as the Dominators.

In last night's midseason finale of Supergirl, The Flash's Barry Allen (Grant Gustin) and Cisco Ramon (Carlos Valdes) popped over to an alternate Earth to retrieve the Girl of Steel (Melissa Benoist) for a team-up that would put Batman and Superman to shame, and in the Nov. 29 episode of The Flash, we'll see exactly what our heroes are up against. (Hint: They're way less cuddly than E.T.)

The idea to tackle the metahuman-hating Dominators came from executive producer Greg Berlanti, according to Arrowand Legendsshowrunner Marc Guggenheim, who was on hand with Supergirland Flashshowrunner Andrew Kreisberg for a press conference with reporters on Monday.

"We all collectively wanted the superheroes to face an external threat. And by external, I don't mean extraterrestrial; I mean not a Big Bad from one of the shows. Rather, a threat that came from outside of the shows," Guggenheim said. "Greg just walked in one day and was like, 'Let's do Invasion.' I think we both had the exact same twin reactions: 'that's totally awesome,' and, 'oh my God, how the hell are we going to do that?'"

Guggenheim admitted that he has a particular affinity for the Invasion comic book storyline that originally introduced the Dominators, which was written by legendary scribes Keith Giffen and Bill Mantlo, with pencils by Giffen, Todd McFarlane and Bart Sears.

"I'm a big Bill Mantlo fan," Guggenheim shared. "That was Bill Mantlo's first work for DC Comics after decades at Marvel, so that particular series looms very large in my personal estimation."

Guggenheim and Kreisberg worked hard to pay homage to Mantlo and Giffen's story in the show, revealing that they originally wanted to portray the terrifying aliens in the same green robes that they wear in the comics.

"When we decided to do all the Dominators full CG as we ended up doing, the robes had to go away because the presence of the robes made animating them prohibitively impossible. But we've got these cool designs of like, 'Oh wow, they really look like the Dominators of the comics,'" Guggenheim said.

While The Flash, Arrowand Legendswill tell an interconnected story centered around the Dominators, the episodes will also keep the momentum going for each show's ongoing plotlines, including last week's Flashreveal that Wally West (Keiynan Lonsdale) now has super speed too.

"At the end of episode 307, Wally became a speedster. That’s huge. That’s big news. To sort of gloss over that and not have anybody react -- considering the myriad of reactions Joe has had to Barry becoming a speedster and Iris finding out -- it felt like we’d be doing a disservice to the people who were watching The Flashand enjoying it," Kreisberg explained. "We didn’t want you to feel, for the people that have been watchingThe Flash,that suddenly their show disappeared for a week while we had all these superhero shenanigans. It was important to advance Wally’s story."

The Flashairs Tuesdays at 8 p.m., Arrowairs Wednesdays at 8 p.m. and Legends of Tomorrowairs Thursdays at 8 p.m. on The CW.

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