"There may be no bulb in the left-hand socket," I suggested. "Or it may be broken."
He nodded. "We'll soon settle that." He unscrewed the bunch of grapes and revealed the double socket, each part of which was provided with a bulb. He exchanged the bulbs and when he pulled the cord the same condition obtained. Only the bulb on the right lighted.
"It isn't broken, you see. Therefore, it must be lighted from some other source. I divined as much when Mrs. Darwin declared she hadn't touched it, and that if it had been lighted from the table she would have seen the person who pulled the cord. The only thing remaining is to find the switch that operates it."
Without a moment's hesitation he made for the safe and I followed him hastily. Now that I was in front of it I saw that the safe was nothing but a closet containing three shelves, which were built into the side walls at such a height that by stooping slightly a man could pass under them with ease. I glanced along the lowest shelf, although I knew that it was empty since Jones' entrance at the inquest, but McKelvie paid no attention to the bareness of the cupboard. He was engrossed in fingering the wall beyond the door. Then with a grunt of satisfaction he caught my hand and placed it where his had been. Instantly my fingers came in contact with a small button. I pushed it, and lo! the left bulb of the lamp sprang suddenly into being.
"Well, I'll be hanged!" I ejaculated, looking at McKelvie. "Why does any sane person want to light his lamp from his safe?" I asked.
"Because, Mr. Davies, it's no more a safe than I am—well—Jenkins," he returned impressively.
"Not a safe?" I exclaimed.
"No."
"Then what—?"
"I'm going to show you." McKelvie again fingered lightly the wall, but this time it was the wall which formed the back of the safe.