The door opened inwards, and presented to the imprisoned men a smooth, unbroken surface, with nothing on which to pull. To push it towards the hall was impossible, as it shut solidly against the frame. Their only hope seemed to split it, but as they gazed at its solid oak timbers this hope died.
‘The window,’ cried La Touche, and they swung round. The sashes opened readily, but outside were shutters of steel plate, closely fastened. Both men shoved and prised with all their might. But Boirac had done his work well. They were immovable.
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.’