"Earth to Invaders: Drop Dead!"

Taking a page from its source material, The CW's "Invasion!" crossover between "Supergirl," "The Flash," "Arrow" and "DC's Legends of Tomorrow" is gearing up for one final blow against the Dominators. Now that Team Arrow has been rescued by the Legends, the heroes of Earth need to come up with a plan to defeat an alien threat that has technology lightyears beyond their own, and a new behind-the-scenes featurette about the final chapter of the crossover explains how they're going to do just that.

RELATED: Final Invasion! Promo Features Supergirl and The Legends

"Episode 7 is the climactic episode of our epic annual crossover between 'Supergirl,' 'Flash,' 'Arrow' and now the 'Legends of Tomorrow,'" executive producer Marc Guggenheim reveals in the video. "It is a beyond-epic conflagration featuring all the superheroes we've established across all four shows fighting alien invaders. It is, quite simply, the biggest hour of television I think we've ever produced."

As seen in the featurette, the heroes of the "Arrow"-verse plan to weaponize their ace in the hole: time travel. Using the Waverider, the heroes will go back in time, kidnap a Dominator and learn what nefarious plans the mind-controlling alien invaders have for earth. The featurette also includes several new clips, including the unveiling of Barry's plan, Cisco's curiosity about Team Arrow's alien abduction experience and Felicity and Cisco's lyrical reaction to the Waverider.

Once in the “Arrow”-verse, Supergirl joined the Flash, Green Arrow, the Legends of Tomorrow and their friends in order to stop an alien invasion. With them, she faced down the Dominators, mind-controlling aliens who have grown so concerned about Earth’s metahuman threat that they have decided to stomp it out before it can reach the stars.

RELATED: Arrowverse Stars Reveal Their Favorite Crossover Moments

“The Flash’s” installment of the “Invasion!” crossover pit hero against hero after the Dominators mind-controlled Supergirl, White Canary, Heatwave, Spartan, the Atom, Firestorm and Speedy to turn on Flash and Green Arrow. Though Flash and Green Arrow were able to restore their friends to their original state, Team Arrow was abducted by the Dominators shortly thereafter, leaving Team Flash, the Legends and Supergirl behind to figure out how to rescue them.

In "Arrow's" installment, Team Arrow found themselves in a simulation where all their dreams had come true. However, this was not a kindness on the Dominators' part, for they had tapped into their brains to discover vital information about the superhero resistance. Fortunately, they were able to break out of the simulation and hijack a space shuttle, only to be rescued by Citizen Steel and the Waverider.

Starring Melissa Benoist as the Girl of Steel, “Supergirl” airs Mondays at 8 pm ET/PT on The CW. The network is also home to Grant Gustin as the Scarlet Speedster in “The Flash,” airing Tuesdays at 8 pm ET/PT, Stephen Amell as the Emerald Archer in “Arrow,” airing Wednesdays at 8 pm ET/PT and Arthur Darvill, Brandon Routh and Caity Lotz in “DC’s Legends of Tomorrow,” airing Thursdays at 8 pm ET/PT.