"A children's adventure, including mermaids, polar bears and an enchanted prince"--Provided by publisher

"Then are we really going?" asked Mary Jane eagerly. "To Boston and Harvard and Uncle Hal's Class Day and everything?" added Alice. Mr. and Mrs. Merrill looked at each other and then at the long letter in Mrs. Merrill's hand. "I do believe we are," said Mrs. Merrill thoughtfully. "That's right!" approved Mr. Merrill heartily. "You'll never regret it. I am sure the girls are old enough to remember the interesting sights they will see and they may never have another chance to go to Harvard Class Day and all the 'doings' Hal writes about." "And then," added Mrs. Merrill, "I always promised brother Hal I'd come when he graduated. One doesn't have a 'baby brother' graduate from Harvard every summer. Though I would like it better if you could go too." "Sure you can't, Dad"? asked Alice, wistfully.

The Bobbsey twins visit Ocean Cliff, the seaside home of their cousin Dorothy. While there they enter the water carnival, play on the beach, and witness a shipwreck.