As old readers know, Winnie Lee and Frank Merriwell were very friendly. As Winnie was of a lively disposition and enjoyed a joke thoroughly, it was not difficult for Frank to induce her to aid him in carrying out his plan. Winnie was all the more ready to do so because she disliked Tom Thornton, who had made himself offensive by having declared that he could "catch" her without a struggle if he so desired, but she was not his style. This had been repeated to Winnie, and she had treated Thornton with the utmost disdain since hearing it; but Frank had urged her to consent to invite Tom to the party that the joke might be carried out, and she finally had consented. For a moment Thornton wondered when he received the invitation, and then he decided that "Grace Darling" must have induced Miss Lee to offer it. Tom little dreamed of the surprising events that were to take place before the evening was passed. CHAPTER XVI. ANOTHER CHALLENGE. Thornton found Merriwell, Diamond, Rattleton and Browning were among Winnie Lee's guests. This he had expected, however, and he was resolved to notice them as little as possible. Willis Paulding was there, and Tad Horner came later, much to Tom's surprise, as he had not known Tad had been invited. There were a number of jolly girls, and Thornton was not long in looking around for Grace Darling. When Tom finally discovered her, to his disgust, she was chatting with Jack Diamond in a cozy corner, which was almost shut off from the rest of the room by portieres. "Hang that fellow!" thought Thornton. "He has been introduced to her, and he has lost no time in getting in his work." As soon as Diamond left the girl Tom hastened to find Winnie Lee, of whom he requested an introduction to "Miss Darling." "Oh, yes!" said Winnie, laughing; "she spoke of you, but I had almost forgotten. I trust you will find her very entertaining, Mr. Thornton." "I am sure I shall," said Tom. "We have seen each other, you know, but have not been introduced." "And she is very particular about that. Being bred in the country, she is not fully conversant with the ways of the world, but she knows an introduction is the proper thing, and she insists on that. There she is." "Miss Darling" was seen chatting with a number of young gentlemen and ladies who had gathered about her. The group scattered as Winnie and Tom came up. "Miss Darling" saw them, and timidly held her fan before her face, peering over it shyly. "Mr. Thornton," laughed Winnie Lee, "it gives me the greatest pleasure to introduce you to Miss Darling." Tom bowed profoundly, while the girl giggled, and made a courtesy. Winnie Lee laughed more than ever. At a distance Frank Merriwell and Jack Diamond were watching. "Will you see Winnie Lee!" softly exclaimed Merriwell. "She is nearly exploding with laughter. She can't hold it. It will be a miracle if Thornton does not tumble."