“Of Two Minds” is episode sixteen of season three of Supergirl.
At City Hall, a woman is giving out cookies, including to the mayor. Who starts bleeding from the nose.
In the previous episode, “In Search of Lost Time”, Supergirl and Mon-El found dead pigeons falling from the sky. Alex is examining one and Imra and Mon-El says this is how it starts. It will soon manifest in people and it’s contagious and 100% fatal. Except this one is not contagious. They must have come in direct contact with Pestilence. The cure is in their DNA and Brainy will extract and weaponize it and kill Pestilence before she comes the Blight.
Supergirl says that’s too aggressive. They tried that with Purity and made it worse. There’s a human side to Pestilence. Imra says they came to end the threat in this time and thereby in the future. Supergirl says they don’t kill people. Imra says these are extreme circumstances.
A stranger enters, but it turns out to be Brainy in a holographic disguise. He nearly caused a riot going out for apple cider vinegar. Winn enters and recognises Brainy anyway. He tells them the mayor, chief of police and city councilmen are all sick. Mon-El, Brainy and Imra will extract the cure whilst the others go check.
Lena is telling Sam how Reign is triggered. In order to find the enzyme that does it, Lena needs to study Reign. Which means electrocuting Sam. Sam ends up in a shadowy valley, and Reign is there. She says they’re coming.
The people are being interviewed at city hall; the mayor has a scratch on his hand and they need to see if others do as well. Supergirl speaks to the woman who was handing out cookies, who’s fine, just scared. Alex and Winn are speaking to a doctor. She wants the quarantine lifted so the patients can be taken for treatment. The c=scratches don’t look new, so J’onn agrees, so as not to cause panic. A panic Imra promptly causes by surrounding the place in a force field. Supergirl gets her to take it down.
Sam tells Lena what she saw, and Lena says it’s a parallel dimension. Where Sam goes when Reign takes over. And because Lena was suppressing Reign, she was there as well. Lena needs more time.
Mon-El is telling Imra they shouldn’t compromise their morals to succeed at the mission.
Supergirl and Alex are talking, and about how Imra might come around, when Winn says he thinks he’s found the one person who came in contact with everyone. The cookie woman. Supergirl heads to where she lives, to find Imra already there and the woman dead of the disease. Because she’s human, not Pestilence. At the DEO, Alex is speaking to Winn when he starts bleeding from the nose. He has it too. And a scratch on his hand as well. The scratches don’t seem to manifest until the illness does.
Supergirl is trying to convince Imra they don’t need to kill Pestilence. Imra tells her she fails. And the Blight happens. And Imra will do whatever it takes to stop it.
Reign is trying to convince Sam to give in, so she will be free. Afterwards, Lena tells her that would condemn Sam to the other dimension forever.
Supergirl ends up doubting whether she will get through to Pestilence, but Imra isn’t telling the whole truth about why she wants to kill her. And the current disease is resistant to the cure for the Blight, because Pestilence isn’t the Blight yet.