The children are excited because on their journey to school, the sea level was nearly up as high as the dock when they got off Skipper Seamus’s dingy. Ruari explains that this is because there is going to be a full moon that night – the moon pulls the sea up even higher at high tide. The class think this is crazy, and decide to go for a picnic at Seal Beach at lunchtime. They have fun playing with Sandy on the beach, but disaster strikes when they find themselves cut off by the swiftly incoming tide. In the nick of time Hermie Crabnik turns up with Skipper Seamus in his dingy to take them back to safety. Later the kids are flabbergasted to meet the Man in the Moon, who confirms Ruari’s story that it his he who makes the tides particularly high sometimes.