A super-powerful alien species has landed on Earth-1 and, in the final part of the epic four-part CW Arrow-verse crossover, we're going to learn exactly why the Dominators have returned to planet Earth: They want one of the team's superheroes.

The Dominators originally showed up on the planet to conduct research to figure out if humans are a potential threat to their planet. The humans of Earth in the '50s didn't pose a threat, but now the planet's population includes meta-humans, Kryptonians, and vigilantes with both high-powered suits and assassin training. In other words, the Dominators aren't willing to wait for the fight to come to them.

Catch up on all this week's Mega Buzz!

So who specifically do the Dominators want and why? They've kidnapped five members of the superhero team for research, to explore the inner workings of their brains. They're targeting one of the heroes in particular, but the bigger question is: Will the team be willing to sacrifice one of their own to save the planet?

Crave scoop on your favorite TV shows? E-mail questions to mega_scoop@tvguide.com or drop us a line at Twitter.com/TVGuide.(Full disclosure: TVGuide.com is owned by CBS, one of The CW's parent companies)