There was a splash over the side of a boat, then another, one more, and a fourth. The water rippled and broke away into smooth curves. Down a long streak of moonlight four dark objects floated above the surface of the waves. For a few seconds there was not a sound, not even a shout, to show that the mermaids were at play.

Two dark heads kept in advance of the others.

“Madge,” warned a voice, “we must not go too far out. Remember, we promised Jenny Ann. My, but isn’t this water glorious! I feel as though I could swim on forever.”

A graceful figure turned over and the moonlight shone full on a happy face. The two swimmers moved along more slowly.

“Nellie, Lillian!” Madge called back, “are you all right? Do you wish to go on farther?”

Phil and Madge floated quietly until their two friends caught up with them.

“I feel as though I could go on all night at this rate,” declared Lillian Seldon. Eleanor put her hand out. “May I float along with you a little, Madge?” she asked. “I am tired. How wide and empty the ocean looks to-night! We must not get out of sight of the lights of the ‘Merry Maid’.”

“There is no danger!” scoffed Madge.

“Look out!” cried Phil Alden sharply. She was swimming ahead. She saw first the sails of a small yacht making across the bay with all speed to the line of the shore that the girls had just quitted.

“Let’s follow the boat back home,” suggested Madge. “We can keep far enough away for them not to see us. It will be rather good fun if they take us for porpoises or mermaids, or any other queer sea creature.”

“Don’t run into that Noah’s ark that we saw anchored in the creek this morning, Roy,” came a shrill voice from the deck of the yacht. “I saw half a dozen women going aboard her this afternoon laden with boxes and trunks—everything but the parrot and the monkey. It looked as though they meant to spend the summer aboard her.”

“Perhaps they do, Mabel,” a man’s voice answered. “The ‘Noah’s Ark’ is a houseboat. It looked very tiny for so many people, but I thought it was rather pretty.”

“Well, we have girls enough at Cape May this summer—about six to every man,” argued Mabel crossly. “I vote that we give these new persons the cold shoulder. Nobody knows who they are, nor where they come from. It is bad enough to have to associate with tiresome hotel visitors, but I shall draw the line at these water-rats, and I hope you will do the same.”

“She means us,” gasped Eleanor. “What a perfectly horrid girl!”

The high, sharp voice on the yacht was distinctly audible over the water. The boat had slowed down as it drew nearer to the shore.

“Swim along with Phil, Nellie,” proposed Madge. “I am going to have some fun with those young persons. I don’t care if I am nearly grown-up; I am not going to miss a lark when there’s a chance. I have that rubber ball that Phil and I brought out to play with in the water. Watch me throw it on their yacht. They’ll think it’s a bomb, or a meteor, if I can throw straight enough. I am going to settle with them this very minute for the disagreeable things they just said about us and our pretty ‘Merry Maid.’”

“Don’t do it, Madge!” expostulated Phil; but she was too late; Madge had dived and was swimming along almost completely under the water. She swam in the darkness cast by the shadow of the boat as it passed within a few yards of them.

Like a flash she lifted her great rubber ball. She had better luck than she deserved. The ball came out of nowhere and landed in the center of the group of three young people on the yacht. It fell first on the deck, and then bounced into the lap of the offending Mabel.

It was hard work for the waiting girls not to laugh aloud as naughty Madge came slowly back to them.

A wild shriek went up from on board the yacht. “Oh, dear, what was that?” one girl asked faintly, when the first cries of alarm had died away.

“Where is it? What was it?” growled a masculine voice. “Are you really hurt, Mabel? You are making so much fuss that I can’t tell.”

Mabel had dropped back in a chair. She was white with fear and trembling violently.

“It is in my lap,” she moaned. “It may explode any moment—do take it away!”

The owner of the yacht, Roy Dennis, turned a small electric flashlight full on his two girl guests. There, in Mabel’s lap, was surely a round, globular-shaped object that had either dropped from the sky or had been thrown at them by an unknown hand. Roy had really no desire to pick it up without seeing it more clearly.

The other girl was less timid. She reached over and took hold of Madge’s ball. Then she laughed aloud. Oddly enough, her laugh was repeated out on the water.

“Why, it’s only a rubber ball!” she asserted. Ethel Swann, who was one of the old-time cottagers at Cape May, ran to the side of the boat. “See!” she exclaimed, “over there are some boys swimming. I suppose they threw the ball on board just to frighten us. They certainly were successful.” She hurled Madge’s ball back over the water, but Roy Dennis’s small yacht had gone some distance from the group of mischievous mermaids and he did not turn back. “If I find out who did that trick, I surely will get even with them,” muttered Roy. “I don’t like to be made a fool of.”

“Don’t tell Jenny Ann, please, girls,” begged Madge, as the four girls clambered aboard the “Merry Maid.” “It was a very silly trick that I played. I should hate to have the cottagers at the Cape hear of it. I don’t suppose I shall ever grow up.”

“Girls, whatever made you stay in the water so long?” demanded Miss Jenny Ann, coming into the girls’ stateroom with a big pitcher of hot chocolate and a plate of cakes. “I have been uneasy about you. You have been in the water for half an hour. That’s too long for a first swim. Poor Tania is fast asleep. The child is utterly worn out with so much excitement. Think of never having been out of a crowded city in her life, and then seeing this wonderful Cape May! Tania wanted to stay up to wish you good night. I left her staring out of the cabin window at the stars when I went into our kitchen to make the chocolate. When I came back she was asleep.”

“Dear Jenny Ann,” said Madge penitently, pulling their chaperon down on the berth beside her, while Lillian poured the chocolate, “it was my fault we were late. The bad things are always my fault. But we are going to have a perfectly glorious time this summer, aren’t we? Just think, next year Phil and I shall be nineteen and nearly old ladies.”

“I wonder if anything special is going to happen to us this holiday?” pondered Phil, crunching away on her third cake.

“Something special always does happen to us,” declared Lillian. “Let’s go to bed now, because, if we are going to row up the bay in the morning to explore the shore, we shall have to get up early to put the ‘Merry Maid’ in order. We must be regular old Cape May inhabitants by the time that Mrs. Curtis and Tom arrive.”

Next morning bad news came to the crew of the little houseboat. Mrs. Curtis had been called to Chicago by the illness of her brother, and Tom had gone with her. They did not know how soon they would be able to come on to Cape May; but within a very few days Philip Holt, the goody-goody young man who was one of Mrs. Curtis’s special favorites, would come on to Cape May, and Mrs. Curtis hoped that the girls would see that he had a good time.

Neither Madge, Phil, Lillian nor Eleanor felt particularly pleased at this information. But Tania, who was the only one of the party that knew the young man well, burst unexpectedly into a flood of tears, the cause of which she obstinately refused to explain.