The CW is about to have its first four-way crossover next week as Supergirl (Melissa Benoist), Green Arrow (Stephen Amell), the Flash (Grant Gustin) and the entire "Legends of Tomorrow" crew band together to save the world from an alien invasion. This week, the network released the first full-length trailer of the crossover, which sees hostile aliens threatening to eliminate the human race.

The trailer opens with a shot of a spaceship heading towards Earth. In Central City, the Flash approaches a crashed ship, and he sees a group of aliens. It is revealed that they are called the Dominators, and later, the Legends are seen battling the same aliens in another location.

"We must exterminate your kind, before the scourge of your planet becomes the scourge of ours," one of the extraterrestrial beings intones.

Barry is told by Iris (Candice Patton) that he can't fight them off by himself, and the speedster says that he doesn't plan to as the camera pans to Oliver, Kara, the Legends, Felicity (Emily Bett Rickards) and Cisco (Carlos Valdes).

Kara learns all the names of her new allies, and she is shocked when she learns about Heatwave's (Dominic Purcell) backstory.

Speaking with Blastr, some of the stars of the network's superhero shows talked about making the crossover, with Amell saying that it starts right at the end of "Supergirl's" hour.

"It was hard work, and I didn't have a day off for five weeks, but there was a spirit of teamwork that made it palatable," said Amell.

Benoist said that filming was "kind of chaotic, but so much fun."

"[There was] an electric energy anytime we were in the same room, especially in our suits," said the actress. "I can't wait for people to see it."

The action will begin right on the tail end of the "Supergirl" episode titled "Medusa" which will see the Danvers celebrating Thanksgiving with Winn (Jeremy Jordan), James (Mehcad Brooks), and Mon-El (Chris Wood). In the promo for the episode, Alex (Chyler Leigh) was just about to come out to everyone when a portal appears in the dining room.

The CW "Heroes vs. Aliens" crossover event begins on Monday, Nov. 28 at 8 p.m. ET on "Supergirl" and continues on "The Flash" at the same time on Tuesday. The third part of the event will be seen on "Arrow" on Wednesday at 8 p.m. ET and concludes on Thursday at the same time on "Legends of Tomorrow."