Torn from their lives as regular kids of overworld miners, Max, Inky, and Luke must now live in a hidden library outpost--underwater! While their parents scramble to safeguard books from the wrath of the evil pillagers, the trio form an adventurous S.Q.U.I.D. Squad for investigating the deep mysteries of the ocean.

Just when they are getting comfortable in their new home, seven librarians are captured and held for ransom by ancient sea-monsters called guardians. Are Inky, Luke, and Max prepared to battle for their family and friends' freedom? Everything they care about is on the line when the kids are forced to face their fiercest enemies in the dizzying maze of an ocean monument. If they can survive the guardians' piercing lasers, outsmart them at every turn, and find their way out of the maze, they might just be able to rescue their people and live to tell about it.

What Max, Inky, and Luke don't realize is that there's another unexpected obstacle to overcome: an ancient, deadly game with high stakes. In this third book in the S.Q.U.I.D. series, these young heroes must join together and use their combined skills and brainpower to survive their most perilous ocean quest yet.