When Lion-O went into the Book of Omens for training, he didn’t expect it to take too long. Now that Snarf has appeared unexpectedly in the Book of Omens, he becomes confused. How is it possible that five years have passed? Better yet what happened that Thundera has become enslaved by Mumm-Ra and his Mutants? Before too much time goes by, Lion-O learns the answers to his questions as well as what has happened to his fellow Thundarians. Now it is a race against time for Lion-O as he must free his friends and defeat Mumm-Ra, before anything worse can happen.