"I recognized you by your big feet," he said in a whisper. "Grace, here's the duplicate key to the laboratory. I had some trouble getting it, but no one knows, and you'll be safe enough. I'll let myself in with the other duplicate key and lock the door. They will be sure to try it at intervals. If you get into any trouble, early in the evening, make a dash for the steps and blow your horn loud. Now, that's all, I think. I'll be hidden in the laboratory until my turn comes. Good-bye and good luck!" In another instant he was off on his motor cycle. Six figures, well disguised in dominoes of as many hues, presently appeared on the ball room floor, just in time for the grand march. It was a pity no one, except the lone teacher, was permitted to look at the brilliant picture. But such was the tradition of the class. After the march, ten ballet girls in tarlatan skirts, their faces concealed by little black satin masks, gave a performance. Following this, a Spanish dancer, whom the six dominoes recognized at once as the treacherous Miriam Nesbit, gave an exhibition of her skill. "I'm going to have some fun with her," whispered the blue domino to the red one. "Just follow me and see." The last speaker joined the dancer as the music struck up a waltz. "That was a good day's work you did for our class, not long ago," she whispered as they danced off together. "What do you mean?" asked the Spanish dancer. "I mean the Black Monks of Asia. Now, do you understand?" "But I thought it was not to be told," exclaimed the dancer, flushing under her mask. "Only to the committee so that you might be rewarded with an invitation," whispered the domino, as she slipped away. "_She_ did confess it, and every freshman in the class shall know it to-morrow!" the emissary exclaimed privately to her friend, the red domino. "In spite of what her brother is doing for us to-night?" returned the red domino. "You are quite right, child. I never thought of that. Perhaps that is the very reason he is helping us get even to-night." "I think it is," added the other, quietly. "Girls, we must hurry up and begin," whispered another of the six dominoes. "They are all going to unmask at half-past ten." So the unrecognized intruders slipped away, stationing themselves about the room. Pretty soon a rumor began to spread among the dancers that there were young men present. No one knew exactly how it started, but it grew and spread with such persistency that it finally reached the ears of the chaperon. "Some of the girls saw their feet," said her informant, "and not only their feet but their trousers, too." The teacher rose and rapped sharply for order. "Young ladies," she called in a loud voice, "I am sorry to disturb the dancers, but we have every reason to believe there are some men in the room. Since it is not yet time for you to unmask, it will be simple to find out who does not belong here by having you file past me. I will lift each mask myself."