Someone, probably Wilkes, Peter guessed, said something in a low voice. "Let 'em hear!" the other replied. "They won't hear much after to-night." Then the voices ceased, and in a few minutes the roar of the engine started.
It seemed to the two who waited in their cell that hours passed. Margaret looked at Peter with a scared question in her eyes. He put his lips to her ear. "Don't forget they had to wait for the signal. "Tisn't as long as we think, Sis. Don't fuss!"
They relapsed into listening silence again. "Difficult to hear above the row of the engine," Peter said.
But he too was beginning to wonder whether any hitch had occurred. Then the shutter slid back, and they saw Michael's face for a moment. Peter went to the door, and Michael whispered: "I'm going to draw back the bolts, but whatever you do, don't come out till you're given the word." He disappeared as he spoke; they heard the bolts drawn cautiously back, and then Peter beckoned Margaret to come and stand out of range of the grille.
Outside in the passage, the four other men had halted behind Michael. A stream of light came from the room beyond Peter and Margaret's cell, and they knew that the men were working with the door open, probably for the sake of air.
Michael gave the signal, and they crept forward.
Michael and Tomlinson reached the door together. "Hands up!" Michael said. "The first man who moves I shoot!"
Even as the words left his mouth there was a report, and the light went out; someone had fired at the electric bulb, and the place was plunged into sudden darkness.
But in that brief moment Michael had had time to see the whole room in one lightning glance. Wilkes was there, working the central machine; the two other men were there, but there was no sign of the Monk.
In a moment there was turmoil. A gun cracked, and the inspector's revolver answered it. Someone's torch lit up a corner of the room for a brief instant, then there was a scuffle in the doorway, another shot, and a wild struggle in the passage. Above the noise of the engine and the fight, Michael shouted: "He's not here! Collar those men!" He felt a shot whistle past his head, ducked, and ran back down the passage, a gun in one hand, his torch in the other.