It's bedtime for the Octonauts until a knocking sound wakes up Kwazii and Captain Barnacles. A snail tells them that a green-blue crab and an orange sea urchin are arguing loudly and keeping the sea creatures up. Shellington explains to Captain Barnacles that a crab and sea urchin as in symbiosis, meaning that need each other for food and protection. Then Kwazii suggests "a break from each other", but they find each other again when Barnacles and Kwazii bump into each other. The urchin relies on the crab, just as the crab relies on him.