Zak and Rory continue their travels around the world's oceans and seas. This time Rory convinces Zak against Zak's wishes to swim in the Mediterranean Sea. Being friendly and inquisitive, Rory gets too close to humans. He is spotted and, being a rare plesiosaur, hunted along with Zak across the Mediterranean until Rory is captured and carried off. Zak must come up with a plan and needs the assistance of unlikely allies to try to free Rory. Zak's plan amazes everyone, but will it work? Will Rory escape to carry on his travels and adventures with Zak?