Angela has organised a cruise on the harbour for herself, Old Tom and Lavinia. However, when Lavinia discovers the boat is an old rustbucket, she refuses to join them, but goes for a cruise on a sleek new yacht instead. On the old boat, Angela and Old Tom aren't having much fun, when suddenly Old Tom catches, with his fishing line, a giant sea monster which pulls him overboard. Angela is terrified, but Old Tom is having the time of his life as the creatures pulls him along, water-skiing, and then gently puts him back on deck. It turns out the sea creature is very friendly so, thanks to Old Tom, the old boat's captain starts up a new enterprise - sea monster rides!