Jal, a new graduate of marine science, is taking a vacation cruise. The ship sinks in a sudden storm. She is saved and taken to the watery depths by two dolphins who bring her to an underwater city peopled mostly by survivors of plane crashes or ship wrecks. Humans and dolphins can communicate telepathically after humans ingest a certain algae. They can breathe underwater after having gills cut into their necks and eating a particular algae. This algae changes the body chemistry so that humans can no longer breathe surface air and must remain underwater. The dolchers (dolphin teachers) instruct the humans how to survive in the water. Each human has his/her own dolcher that they bond with for life. People live in a dome on the ocean floor. The buildings, clothing, everything comes from what they can salvage from downed planes or ships. The underwater society is similar to that of the land in that there are good and bad people. Lawbreakers are banished to an area where they are happier or the open ocean when they can't behave. Jal meets her soulmate, Arn, who becomes her guide to travel to other domes in search of what can reverse the effects of the algae and to educate her about her new world.