"Where was it?" Davis showed him. Gerrod put one hand on the spot and struck a chord tentatively. His expression changed from weariness to hope. "Wait a minute!" he exclaimed, and darted into the laboratory, to return a moment later with half a dozen test tubes full of the sticky animalcules. "We'll put another one there and strike a chord." He did so. The contents of the test tube remained unchanged. He struck another. Still no change. Then, deliberately striking one key after the other, with the eyes of all four of them fixed hopefully on the test tube, he began to go up the keyboard. Note after note was struck, but just as they were about to give up hopes of finding the cause of the first tube's clearing Gerrod struck a key--the _F_ above high _C_. The instant the shrill note sounded out the test tube clouded--and was clear! It had lain upon the sounding board of the piano. The vibrations of the piano string had been communicated to it through the sounding board. "_Done!_" shouted Davis at the top of his voice. Nita was speechless. "Sympathetic vibrations," said Gerrod happily. "If you could hang up one of those microscopic shells and ring it it would ring that note. So, when the vibrations from the piano strike them, they vibrate in sympathy, only the piano vibrations are so strong and the shells so fragile that they rack themselves to bits, and the animals are killed. Whee! Hurray! Hurray!" He shook hands all around, hardly, able to contain his excitement. "But I say," said Davis anxiously, "will those vibrations travel through water, and can we put a piano overboard?" Gerrod laughed. "We'll put a submarine siren overboard," he said excitedly, "and tune it to that note. You can hear a submarine siren for fifteen miles with an under-water telephone. Man, you've done the trick!" The maid appeared in the doorway. "Some one on the telephone for Miss Morrison." Nita reluctantly left the room where the others were chattering excitedly. She went to the telephone and put the receiver to her ear, still unconsciously trying to catch the words of the party in the music room. Almost the first words she heard drove them from her mind, however. Her father was speaking. "Nita," he was saying coolly, "this is your father. I'm marooned in the house on the island, and the Silver Menace is climbing up the walls. The windows are blocked. I'm expecting them to break in any minute. When they do I'm done." "Daddy!" Nita choked, aghast. "Simmons, the chauffeur, tried to get across the bridge this morning," said her father still more coolly, "and the sticky stuff got him. The room I'm in is dark. The Silver Menace has climbed up to the roof. We've stopped up the chimney so it can't come down to get us, but when the house is completely covered we'll be in an air-tight case that will suffocate us sooner or later. I'm rather hoping the windows will break in before that time. I'd rather die like Simmons this morning."