'Supergirl': Breaking Down the Ending of "Fallout"

True to its title "Fallout", tonight's episode of Supergirl dealt with the repercussions of President Olivia Marsdin's being outed as an alien in the Season 4 premiere -- and one of them will be a major issue for National City's hero.

Spoilers for tonight's episode of Supergirl, "Fallout", below.

Otis Graves wasn't wrong when he said a fuse had been lit last week. With her secret out, President Marsdin steps down from the highest office in the land but the anti-alien sentiment that seemed to be fringe last week has now spread. Of course, Supergirl is determined to keep the peace and it's something that poses a problem for the enemy she hasn't even met yet -- Agent Liberty. He tells Mercy Graves that it's clear the Girl of Steel is going to be an issue, but Mercy has a plan for that in the form of a vial of Kryptonite.

We don't see the full extent of Mercy's plan until the last moments of the episode, however. After being captured at L Corp by Supergirl, Mercy is locked in a DEO cell where Agent Jensen is tasked with keeping an eye on both Mercy and Otis and reporting back to Alex hourly. Of course, it's not going to be quite that simple. It would appear that being captured by the DEO was exactly part of Mercy's plan as she already is aware that Jensen harbors his own anti-alien sentiment. She quickly appeals to that and before we know it, Alex discovers that Jensen along with both the Graves siblings are gone.

And they didn't escape the DEO alone. They've gotten their hands on the device used back in Season 2 to put lead into the atmosphere and drive back the Daxamite invasion. This time, however, it's not lead the device is going to be loaded with. Mercy puts the vial of Kryptonite into the device, sending it into Earth's atmosphere. Above National City, Supergirl breathes in the tainted air and quickly plummets to earth, gravely ill.

So if Supergirl can't breathe Earth's air, how is she going to fight for justice and help save the world from the anti-alien radicals this season? The answer to that is something that may have already been teased, thanks to the teaser trailer shared at San Diego Comic-Con earlier this year. In that trailer, a figure appears in the darkness with the familiar red and blue of Supergirl's costume, but instead of being the familiar cape, it's an armored look, complete with a mask and glowing, light up chest sigil. With Earth's air now polluted with Kryptonite, it will be impossible for Supergirl to breathe unless she has some sort of way to protect herself. The armored, fully masked and helmeted costume would be exactly the sort of thing that would protect her from the Kryptonite poison and allow her to continue to fight against the injustice and hatred sweeping across the nation.

As for where Supergirl gets that new suit, that remains to be seen and while it's likely that it will be a creation from the DEO -- possibly even with future technology courtesy of Brainy -- tonight's episode did give viewers a look at parts of Lex Luthor's war suit in action thanks to an intense shoot-out between Lena and Mercy in the basement of L Corp. Considering that it was L Corp that created the device that was used to poison Supergirl tonight, it's not impossible that Lena could re-work the war suit to help Supergirl stand up for justice once again.

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