The S.Q.U.I.D. squad / Miller, Megan

"When Pillagers establish an outpost not far from the Book Guardian's hidden ravine headquarters, it's time for the S.Q.U.I.D Squad to swim into action. When their plans to outwit and scare the Pillagers fail, they must turn to the help of a mysterious captive of the Pillagers, the Talker. But the Talker seems to have devious plans of her own"--Back cover.

"Torn from their lives as regular Librarian's kids, Max, Ingrid, and Luke must survive in a hidden Librarian outpost-underwater! While their parents scramble to safeguard the books of the Overworld, the trio sneak out of their warren of underwater caves to investigate the deep waters of the oceans. When they hear about the Legend of the Coral Caves, a trove of golden coral beyond imagining, Max, Luke, and Ingrid realize that this wealth could help solve all their problems. Now it's up to them to find the cave and bring the fortune back to save their families-and their books!"--Provided by publisher.