"I don't want to worry Dave or the others," said Ben. "But I think somebody ought to be told." "Told what?" asked the senator's son. "About Nat Poole. I got the word from a friend of mine, Joe Devine. Joe was talking with Nat Poole, and he said Nat was very angry at all of us, and angry because Mrs. Wadsworth was giving us the party, especially as he wasn't invited. Joe said Nat intimated that he was going to make the affair turn out a fizzle." "A fizzle?" queried Phil. "How?" "Joe didn't know, but he told me, on the quiet, that I ought to watch out, and ought to warn the others. But I don't like to say anything to Mrs. Wadsworth, or the girls. You see, it may be only talk, and if it is, what's the use of getting the ladies excited?" "It would be just like Nat to play some dirty trick," said the shipowner's son. "The question is, What will it be?" "Somebody ought to stand guard," was Roger's advice. "And I think we ought to tell Dave." This was readily agreed upon, and Dave was told a few minutes later. His face at once showed his concern. "It mustn't be allowed!" he said, earnestly. "I don't care so much on my own account, but think of Mrs. Wadsworth and the girls! Yes, we must keep our eyes open, and if anything goes wrong----" He finished with a grave shake of his head. "What are you boys plotting about?" asked Laura, as she came up. "Come, it won't do to stick together like this, with all the girls arriving. Dave, go and make folks at home,--and you do likewise," she added, with a smile at Phil and Roger. The boys dispersed and mingled with the arriving guests. Dave did all he could to make everybody feel at home, but all the while he was doing it he kept his eyes wide open. Presently, chancing to look in the direction of the automobile house, Dave saw somebody skulking along a hedge. The person was visible only a second, so the youth could not make out who it was. "Maybe it's all right, but I'll take a look and make sure," he told himself, and excused himself to a girl to whom he had been talking. As he hurried across the lawn he passed Phil. "Come with me, will you?" he said, in a low voice. "See anything?" demanded the shipowner's son. "I saw somebody, but I am not sure who it was." Taking care not to make his departure noticeable, Dave walked toward the automobile house and Phil followed him. Soon the pair were behind some rose bushes and then they gained the shelter of the heavy hedge. "There he is!" said Dave, in a low voice. "It's Nat Poole, sure enough!" "What's he doing?" asked Phil. "Nothing just now. But I guess he is up to something." Keeping well out of sight behind the hedge, the two boys watched the son of the money-lender. Nat was sneaking past the automobile house and making for a washing-shed adjoining the kitchen of the mansion. "I think I know what he is up to," murmured Dave. "Come on after him, Phil."