The S.Q.U.I.D. Squad is made up of three bold children who are part of a secret, underwater society of Book Guardians. They combine their unique talents to solve mysteries, right wrongs, and explore the oceans!

With their secret base discovered, the Book Guardians, bent on protecting their culture, must find a new headquarters far from the Pillagers. As they set out for the Ocean's End, a faraway, uncharted sea, a surprise Pillager attack splits the voyagers up. It is up to the stranded S.Q.U.I.D. Squad to save the library of ancient books that the Pillagers want to burn and find their way to their new base.

A mysterious underwater witch sends them on a dangerous path through swimming skeletons and poisonous sea pickles, but the witch's magic spells--from super-fast swimming potions and endless invisi-food--may cause more problems than they solve. With the fate of their community resting on their shoulders, Inky, Max, and Luke will use everything they've got to outsmart the Pillagers.