Jules, a ten-year-old introverted and imaginative boy beset by lingering self-doubt, is used to being the butt of classroom jokes--that is, until he must find the inner strength and confidence to cross a perilous world and rescue his mother from the clutches of an evil count. Unlike his classmates, Jules dreads the upcoming school break, and is sure his summer will be spent performing tedious chores in the family bean store. But when he unexpectedly captures a pint-sized, trash-talking troll named Bergen under a gardening bucket, he is drawn into a mystical world hidden deep in the woods behind his home, a world full of unimaginable splendor that sprouted from Jules's own mind when he was shown a magical three-dimensional holographic map by a council of trolls, gnomes, and other mysterious creatures. When his mother is kidnapped by the evil Count Barchmod, Jules must set out across this strange and treacherous landscape to exchange the map for her freedom. Accompanied by Bergen and an eight-year-old neighbor named Betsy who has run away from home, Jules races to reach the count's fortress before it is too late. Along the way, Jules and his friends must evade tunnel-dwelling ape-men, cross a desert with a caravan of human-sized ants, and sail across a great inland sea on an antiquated ship manned by a rough-edged crew-all while being pursued by a swarm of giant insects with a collective consciousness that is determined to get the map for itself. And when he's confronted by the truth about his parents, Jules wonders if all his efforts will be futile. The Crystal Sea relates the conclusion of Jules's adventure, which began with the separately-published book titled The Map of Eternity.