The third book in the Siren Anthology, Treading Waves, picks up just months after the second where Santi and Rogan are still reeling from the tragedy that struck in the last book. They are trying to cope and find how they fit into this new world while outside forces are sabotaging them and trying to use them for ill-gains. The reader also learns more details about how this underwater world was built and, how Santi and Rogan may be able to fix the current, horrible, state of affairs.