Summer of the Sea Serpent

In a land lost in mist, in a time before time, there is a powerful Sword of Light. Merlin the magician needs that sword for the good of all Camelot. He turns again to Jack and Annie for help. With only a rhyme to lead them, Jack and Annie set out on a journey filled with fabulous creatures. But can they solve the ancient riddle before night falls? Part of the Magic Tree House Merlin Missions series.