A team of marine biologists, led by researcher Marla S. Rowland, brave the rocky waters of Jeju Island, South Korea in hopes of conserving a merrow (mermaid) population that's been driven to near extinction via human hunting. The team has been betting on one dominant female, Astra, to bear most of the responsibility in her largely male pod. They captured Astra when she was a genderless merling in 2001 to protect her from drive hunting and released her back into the waters after she hit sexual maturity. Marla and her crew has been monitoring and protecting Astra and her pod ever since. Ten years after her initial capture, though, Astra still hasn't birthed a single child. That summer of 2011, they find her beta male, Alto, on the shoreline, looking shriveled and "lovesick." The team rehabilitates and releases him, taking Astra back at the same time for a health inspection and a fertility shot. When Astra's released, she has sex with her alpha male, Triton, in front of the scientists. Despite beta males' typical exclusion from intercourse, she invites Alto as well. The threesome ends with Triton in between Alto and Astra. It's noted that Triton and Alto used to be "kissing pals" when they were merlings, and that pals usually bond for life. Of course, this was platonic— in 2011, it was unheard of to for merrows to be homosexual. After this rare instance of exhibitionism, Astra lays her first fertile egg. The scientists are ecstatic and take the egg to raise in captivity, where Alto only watches them. Weeks later, the research facility receives a tip about Astra's location, who's been missing since her egg was taken. The team finds her and Alto in a fierce battle. Astra escapes when the team arrives, though not without them seeing her grief and fury. They take Alto and Triton in and realize Triton is changing into a female, and Alto is changing into an alpha male to take Triton's place in their triad. The team experiences a trio of tragic revelations. First, they realize the egg is not Triton's but Alto's, which means Triton was most likely infertile. Despite the egg being his, Alto lets the team take it because, second, Alto is homosexual. His only loyalty was to Triton, who he now cannot love because Triton is a female. Finally, since the alpha male of a trio experiences a sex change when the dominant female's health is failing, they understand Astra is sick or about to die, potentially from grief over her child being taken. The scientists, with the loss of their star hanging over their heads, grapple with the big question: why would Astra keep an infertile alpha and a gay beta male as her two mates? One group decides Astra had a helpless fondness for the pair. The other argues that they're projecting humanity on Astra yet again and that the scientists were more foolish than Astra for doing so. Later, a report of a merrow corpse, presumably Astra's, whose cause of death is undetermined, is discovered.