In the Curse of Lake Osis, volume 2 of the Osis Fantasy Trilogy and sequel to the Black Pearl of Osis (vol. 1), the evil Black Pearl has again fallen into human hands, and Jonathan and Magenta are summoned by Master Cobalt to find and destroy the Pearl. Together with their guide, Bruno, a strange, mute boy, and the magic skipping ropes as their weapons, they leave for Pebble Island where Commander Sepio, the new owner of the Black Pearl of Osis, resides with his army of Warriors. But Bruno seems to have plans of his own. He often disappears, which makes Jonathan and Magenta suspicious of his loyalty. When Bruno abandons them, they lose their way and fall into the clutches of a lone Warrior, Fonsta and his savage companions, and a deranged King Leyon. They are relentlessly pursued by a mysterious, vicious dog; they adopt a monkey on their way and nearly drown crossing Lake Osis. When, at the end of their journey, Jonathan and Magenta confront Sepio and the Black Pearl, they find themselves trapped and must use all their wits to outsmart the enemy. While events unfold, they discover the secret of Bruno's plan, which leads to tragic consequences.