In the third book of the series, Mark's mom, Samantha, and his older brother, Michael, discover the secret that Mark has been hiding from them for the past several months. Invited to Mindar by the Royal Princess Nadee, Mark's family is enjoying their visit to the amazing underwater city. That is, until a friendly seahorse race takes a very unexpected turn when they are suddenly transported to the savage and barbaric world of the Octopi, a race of half-man, half-octopus creatures. They will gain some very surprising allies in their fight against the Octopi, but will that be enough to get them all back safely to Mindar?