In spite of all the mysteries, however, and there certainly seemed to be a good many, the boys slept like tops in their attic-room that night. Perhaps it was as well "for their brains' sake," as Peter remarked, for they woke next morning to yet another mysterious affair.  
This time Jan had a story to tell, a story of noise. "A most peculiar noise, from the wall I think it was, or from the floor, Brownie, but I couldn't make out," she announced at breakfast-time. "Were you walking about in the night?"
 
"No, indeed, my dear," said the old woman.
 
"And you needn't ask us, for we didn't move all night," Peter assured her. "After all, there's something to be said for a jolly comfortable feather-bed after a week's outside camping. Though, of course, I'd rather sleep out of doors any day (or night, of course, I mean) than in a house."
 
"Well, I don't know what my noise was then," said Jan; "I was hoping it was one of you. I am sure I was awake a whole hour listening to it and wondering. Like a banging and a tinging it sounded."
 
"Ting! ting! d'you mean? Why! perhaps it's like my noise," broke in Peter again, staring, "like the noise I heard when we were sleeping in camp."
 
"Brownie, do you know what it was?" persisted Jan. "Have you ever heard it before?"
 
"A noise, my dear, there once was, that some said——" the old woman checked herself. "Never, Miss Jan, have I heard such a sound as you name. Mice now, dearie, they make queer sounds," she added earnestly.
 
"But mice don't bang or ting," Jan remarked to Peter as they made their way again towards the camp. Somehow the three didn't feel satisfied about the matter. Robin certainly said little enough, but he "probably thought the more," as the others remarked. "We'd come down to your room and listen if it wasn't so rippingly fine," remarked Peter, "but the wind's veered right round and jolly weather's going to set in, though one doesn't know how long it will last with the suddenness of it. So it'd be downright silly to sleep indoors again, wouldn't it, unless you're really funkish, of course," he added considerately, "if you are——!"
 
"Of course I'm not," said Jan bravely. After all, the fright of the night before had quite vanished with the morning light. She began to think that perhaps she had imagined the whole thing. "You see, after Brownie being so mysterious," she said, "and—well, everything,—I think perhaps I was just a bit silly."
 
"Righto! I expect it was that," said Peter in brotherly tones as all three made their way down to the pioneer hut.
 
The sound of Mrs. Vaughan's horn called them, however, before they could set to any kind of work. Every morning during the ten days' camp she had come to speak to them, and every day the bulletin had been a satisfactory one. Dick's scarlatina case seemed certainly to have been a very slight one, and nursing had not been arduous. To-day, as they rowed across, Mrs. Vaughan was looking extra cheerful and pleased.
 
"Yes, Dick's still progressing," she said; "he's really tired of being in bed, and he'll be up as soon as the rash has disappeared. Peeling will come next, I suppose. I've a piece of news for you to-day, however, which I had better give at once. Can you guess?"
 
"Anything about Dad?" asked Peter.
 
"No, it's Donald. He's out of quarantine now; it's ten days since he saw Dick, you see, and he's evidently not going to catch scarlet fever. So I thought of a plan which will, I hope, give pleasure to you all. I wrote to your aunt and told her what you three were doing, and suggested that Donald should join you on the Island. He's coming down to-morrow; I heard to-day. What do you think of that?"
 
"Mother, it's perfectly ripping. What a splendiferous idea! And—we never thought of it!" There was no doubt about the satisfaction of the three.
 
"Well, it's really a little hard on all of you, Donald as well, to have your holiday changed by the scarlet-fever business, so," Mrs. Vaughan smiled. "I'm glad you all approve. I spoke to Brown, and he was sure Brownie would welcome another. If seems that you're all more of helps than hindrances, he says, to his wife, and I'm glad to hear it. So another Scout will be no trouble to the old folk, I hope. The attic where you boys sleep is so big that another trundle-bed can be rigged up there, if there's a wet night again."
 
"If! But I hope there won't be," said Peter, as they made their way back to camp. "I say—ripping, isn't it? We don't know him, but——"
 
"Well, we know that he's a Scout," said Robin.
 
"So he's sure to be thoroughly decent," said Jan, who adopted her brother's expressions when in need of extra words.
 
And certainly Donald proved in the opinion of the three to be indeed "thoroughly decent" when, next afternoon, he arrived; a "jolly all-round man and a good Scout" the boys voted him, and Jan was quite as satisfied. Within an hour of his arrival he had been introduced into all the plans of the campers, and the four were seated round the fire roasting potatoes for supper as though they had been boon companions for years. "And you've the Pioneer Badge already?" exclaimed Robin, "as well as the ones we've got. And,—what's this?—Oh! the Signaller's Badge"; the boys were examining the proficiency badges that Donald wore on his right arm.
 
"Well, Dick's a better signaller than I am," said Donald; "I wish he was here. He's jolly good and quick at flag-wagging; you should see him at it, and——"
 
"You're both frightfully clever, I expect," said Peter. "Oh, I say, being cousins, you know, and all that, d'you think, Robin, that we could ask him about the mysteries?"