'Supergirl': "American Alien" Ending Explained

Supergirl's fourth season is officially underway, and the debut episode gave fans quite a lot to process.

Spoilers for tonight's episode of Supergirl, "American Alien", below!

The episode saw Kara Danvers/Supergirl (Melissa Benoist) coming into her own as Earth's main Kryptonian protector, a task that brought a whole new problem to light. Unbeknownst to Kara, a "Human First" hate group had begun to emerge, with Agent Liberty (Sam Witwer) and Mercy Graves (Rhona Mitra) appearing to be at the lead. This group was responsible for several hate crimes towards aliens, culminating in them attempting to attach an alien summit led by President Olivia Marsdin (Lynda Carter) at Camp David.

While Kara and company were able to stop the attack, the fallout of the event proved to be quite a lot -- and we're here to break it down.

First, cable news made a discovery from the footage of the Camp David attack -- namely, where President Marsdin briefly revealed her Durlan identity, unmasking herself as an alien to the public. As the news report pointed out, this confirmed a theory that the "Human First" group had already held, which theoretically will only cause the movement to grow more.

Next, Mercy and Agent Liberty were seen with Fiona (Tiya Sircar), the leader of an alien therapy group who they had kidnapped. As Mercy and Agent Liberty began to talk about how the Camp David attack went well, Liberty proceeded to kill Fiona, as another way to send a message.

And finally, the episode went back to one of Kara's heroic feats from earlier in the episode, where she saved a train from falling off of a cliff in Kasnia. Underneath the cliff and the frozen train, a rumbling could be heard -- where the alternate version of Kara from the Season 3 finale appeared to be training.

This reminder of the alternate version of Kara will surely complicate things in some way, especially knowing that the plotline is set to be a take on Superman: Red Son.

"For fans of the comics, I think they might recognize that the story we want to tell is inspired by the iconic DC Comics' Red Son, which told an alternate origin story for Superman," executive producer Robert Rovner explained earlier this year.

"What happened if — as a baby — Superman landed in Russia and became a hero there instead of in America?" executive producer Jessica Queller added. "It's an homage to that."

There's no telling exactly how the anti-alien sentiment and the Red Son of it all will intersect as the season goes on, but it's safe to say that both will pose an interesting challenge to the Girl of Steel.

"This season they really want to thematically tackle more topical stories that maybe mirror what's going on with the state of the world and our country." Benoist said in a recent interview. "There's a lot of anti-alien sentiment at the beginning of Season 4 that Supergirl is going to have to grapple with. I think their main premise is that fear itself is a villain and can hope conquer it? Supergirl stands for hope, so we'll see. I think fear is her biggest opponent yet because it's more of a wildfire-type emotion."

What did you think of Supergirl's Season 4 premiere? Share your thoughts with us in the comments below!

Supergirl airs Sundays at 8/7c on The CW.