Book's homeworld Kwejian is threatened by Osyraa of the Emerald Chain, who wants the freed Andorian Ryn returned, and Discovery intervenes.
Book receives a call from his brother Kyheem: their homeworld Kwejian, its climate disrupted by the Burn, is being devastated by locust swarms. Kyheem has made a deal with Osyraa, leader of the Emerald Chain, trading access to Kwejian's trance worms for help, a choice that has opened a rift between the brothers. Because Emerald Chain aid tends to bring ruin, Discovery is permitted to go to Kwejian. Osyraa's real price is Ryn, an Andorian who escaped her service, and Kyheem agrees to defy her if the Federation helps against the locusts. Using Book's ship, the crew blocks Osyraa from taking Ryn, and although she sees through the ruse, she withdraws, vowing revenge.
Meanwhile, Georgiou suffers blackouts and flashbacks, the first signs of the condition that will end her time aboard Discovery. The episode brings Osyraa on screen and sets up the season's coming confrontation with the Emerald Chain. Jonathan Frakes directed.