Agana Taitano Hofstadter, a brilliant expert in cryptanalysis, is summoned to Ennea, a dark and inhospitable planet, shrouded in mystery, whose only inhabitants are the enigmatic Enneans. Joining her on this journey to another star system is a diverse team of human and dolphin scientist-explorers, including an arrogant cybernetically enhanced human, an artificial intelligence with a proclivity for holographic antics, and Taitano's dolphin mentor. As she struggles to manage a debilitating psychological condition, Taitano soon uncovers a world-changing conspiracy deep within the subterranean ocean of Ennea. In a race against time, Taitano and her colleagues must work together to save the Enneans­, and themselves, from certain destruction.