Alan, an American scientist in South America studying parasites, is reading a letter from his wife which mentions that his friend Barney sent him a series of clippings about something called the Intertropical Convergence Zone. There seems to be something causing men to kill their wives and children, possibly connected to the parasites in the caneflys Alan is studying and a cult in the US called the Sons of Adam. The cult kills all women, claiming they do it for God. In one news clipping sent to Alan, there was the story of a caravan of doctors visiting the cult's breakaway community and the murder of the one female doctor who had tagged along. Barney and Alan come to the conclusion that there was something causing a psychosis in the men that drove them to kill their wives, and a religious leader popped up to explain it.

Alan's wife, who is sending him letters about the situation as it evolves in the US, is getting worried. No one is publicly taking the threat seriously and her female friends are disappearing. Upon receiving this letter, Alan decides to immediately head home to protect his wife.

In the Miami airport on the way north, Alan found most of the planes crammed and with no open seats. He calls his wife Anne and they chat for a minute, both feeling a little better. Alan notices that many women are wearing baggy clothes, parkas, ponchos, anything to cover themselves up. Men are acting normally but the women and children are palpably afraid. Especially as some men are handing out cult propaganda. Newspapers show that funeral homes were refusing female corpses and women's bodies were being dumped into the sea so much that they impeded traffic. It seems that the outbreaks of femicide are happening around the globe but only in certain latitudes and it has no scientific explanation so far. They just seem to be manias sweeping certain parts of the globe.

Taking a break from reading the news, Alan thinks about his wife and child he hasn't seen in months. He fantasizes about the night he will spend with his wife until he realizes he's holding his pocket knife in his hand and he was in fact fantasizing about murdering them. He calls Anne in a panic, telling her to get Barney and take him to the lab when he gets home so they can study him and protect her. Later scientists theorize there is a connection between the sexual and the violent within men, specifically surrounding adrenaline, that could explain the manias.

Alan gets home and warns his family away, going instead to stay at the lab. Anne takes Amy and they escape dressed as men and boys. But men in these newly "Liberated Zones" that are popping up further and further North are catching on to that fact Anne's a woman. She decides to hide as best she can, but knows she has to move South for the winter or she'll freeze. Anne thinks she saw someone at her old hiding place, collecting something in a sample tube. It makes her think of the experiments her husband conducted on flies and mosquitos, killing off half the population so that the species can die off and stop being so terrible.