'Supergirl': Third Worldkiller Revealed in "Of Two Minds"

In tonight's episode of Supergirl, Pestilence made her presence known with a mysterious illness making people gravely sick in National City. However, it wasn't just her deadly powers that emerged as Team Supergirl soon discovered the identity of the third Worldkiller.

Spoilers for tonight's episode of Supergirl, "Of Two Minds", below.

As fans got a hint of last week, Pestilence arrived in National City. First it was dead birds falling from the sky, then it was people at a National City bank, before finally the lethal illness struck Supergirl (Melissa Benoist) painfully close to home -- Alex (Chyler Leigh) and Winn (Jeremy Jordan) both fell gravely ill. Brainiac-5 tries to come up with a cure for the illness, but they quickly discover that they need Pestilence's DNA to make it work. How do you get DNA? You identify the Worldkiller and after getting it wrong once -- a young woman who had been handing out cookies prior to the infection at the bank turned out to be just another victim -- the third Worldkiller is revealed to be Dr. Grace Parker, the doctor who was treating the victims at the bank.

Supergirl, along with Mon-El (Chris Wood) and Imra/Saturn Girl (Amy Jackson) set out to stop her. Supergirl, ever optimistic, thought she would be able to get through to Grace by appealing to her humanity but it turns out that, unlike the human side of Purity, Grace wanted to give in to Pestilence. There is no talking her down and after a fight in which Pestilence injures and infects Supergirl, Imra encapsulates her in a force field and attempts to kill her with a special dart. Unfortunately for Team Supergirl, Purity shows up and saves Pestilence, giving the dying Worldkiller strength and flying away. Imra was able to collect DNA, though, so that all infected by Pestilence this time could be saved.

Pestilence getting away was a huge blow to the team, but it wasn't the only painful turn in the episode. The team tracks Pestilence and Purity to L-Corp and arrive only to discover that Lena (Katie McGrath) had Sam in a lab, but before any explanations can happen, Purity and Pestilence show up. The pair team up and Sam disappears, Reign standing in her place. The three Worldkillers now united quickly take out the heroes and leave, Supergirl in shock at discovering her greatest enemy is one of her closest friends.

The stunning reveal -- not just of the third Worldkiller's identity, but of Reign's identity -- sets up for the showdown between the Girl of Steel that Supergirl has been building towards all season and, according to executive producer Robert Rovner, that face-off will be coming sooner rather than later and will be epic.

"It's going to be epic," Rovner told Entertainment Weekly's Spoiler Room. "What's great about this season is that what makes it powerful and exciting is that it's really emotionally charged. Because the final solution is about saving your friend, it focuses on how they'll accomplish that."

But what is that final solution? That's something that Odette Annable, who plays Sam/Reign, told ComicBook.com earlier this year might be bittersweet.

"Maybe I'm being optimistic when I say that I think there is a way to separate the two," Annable said. "I don't know how. I don't know if it's possible. I don't know what the stronger storyline would be. Because I certainly see -- and this is all just me taking random stabs here because I don't know what's gonna happen -- but I do think that there's strength in Sam giving up her life to do what's good for humanity, then having Reign gone. I also think that having a redemption arc, of a sort, of having Sam saved, especially for her daughter, I think that would be a really nice ending. So, I'm gonna go with that one."

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

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