From the introduction: There are four high priests in Ampai, each generally having an apprentice, representing and defining the four quarters of the city. The priests have to complete a challenge to even become an apprentice – they must show they are one with the sea and that they can correctly care for its creatures. The prospective apprentice must collect an intact mermaid’s purse, requiring a deep dive, and raise the shark within as their own, guiding it as they will have to do with the jellyfish.