As they stood panting and baffled, Mallet’s eye caught the switch of the electric light. It was off. He clicked it on. Though no answering flood of light poured down, he noticed something that interested him. ‘Your torch, La Touche!’ he cried, and then he saw what it was. Tied to the switch was a length of fisherman’s gut. Practically invisible, it passed down the wall and through a tiny hole in the floor. Any one pulling it from below would switch off the light. ‘I don’t understand,’ said La Touche. ‘That means he had a confederate?’ ‘No!’ cried Mallet, who had been looking about with the torch. ‘See here!’ He pointed to the chair Boirac had occupied and which now lay on its side on the floor. Fastened to the left arm was another end of gut which also entered a hole in the floor. ‘I bet those are connected!’ Their curiosity temporarily overcame their fears. La Touche turned on the switch and Mallet, pulling the gut at the arm of the chair, heard it click off again. ‘Ingenious devil,’ he muttered. ‘It must go round pulleys under the floor. And now he has cut off the current at the meter.’ ‘Come on, Mallet,’ La Touche called. ‘Don’t waste time. We must get out of this.’ Together they threw themselves on the door with all the weight of their shoulders. Again they tried, and again, but to no purpose. It was too strong. ‘What does it mean, do you think?’ panted Mallet. ‘Gas, I expect. Perhaps charcoal.’ ‘Any use shouting at the window?’ ‘None. It’s too closely shuttered, and it only opens into a courtyard.’ And then suddenly they perceived a faint odour which, in spite of their hardened nerves, turned their blood cold and set them working with ten times more furious energy at the door. It was a very slight smell of burning wood. ‘My God!’ cried Mallet, ‘he’s set the house on fire!’ It seemed impossible that any door could withstand so furious an onslaught. Had it opened outwards, hinges and lock must long since have given away, but the men could not make their strength tell. They worked till the sweat rolled in great drops down their foreheads. Meanwhile the smell increased. Smoke must be percolating into the room. ‘The torch here,’ cried La Touche suddenly. Taking his pistol, he fired a number of shots on the bolt of the lock. ‘Don’t use them all. How many have you?’ ‘Two more.’ ‘Keep them.’ The lock seemed shattered, but still the door held. The men’s efforts were becoming frenzied when Mallet had an idea. Along the farther wall of the room stood a heavy, old-fashioned sofa. ‘Let’s use the couch as a battering-ram.’