Secret of the River by Fred M. White

Murray's concern seemed so genuine that, for a moment, even Nevil, hiding in the big oak buffet, was deceived. But only for a moment before he began to see that there was something quite sinister in this business than appeared on the face of it. Meanwhile, the Croft was all bustle and confusion. The library emptied and Nevil could hear all sorts of directions going on outside on the terrace until voices died away in the distance and he deemed it safe to crawl out of his retreat and make his way to safety by way of the window. He half turned as he saw a figure standing there, faintly outlined against the darkness.

"It's all right, sir," the man standing there said. "It's Jakes. I thought I would stay behind until you were clear, in case of accidents.