The Camera Fiend by E.W. Hornung

"So," said Dr. Baumgartner, "you not only try to play me false, but you seize the first opportunity when my back is turned! Not only do you break your promise, but you break it with brutal violence to a young lady who has shown you nothing but kindness!"

Pocket might have replied with justice that the young lady had brought the violence upon herself; but that would have made him out a greater cad than ever, in his own eyes at any rate. He preferred to defend his honour as best he could, which was chiefly by claiming the right to change his mind about what was after all his own affair. But that was precisely what Baumgartner would not allow for a moment; it was just as much his affair as accessory after the fact, and in accordance with their mutual and final agreement overnight. Pocket could only rejoin that he had never meant to give the doctor away at all.