midnight
`` Monsieur , '' said the old man , `` I do not sleep at all . I watch . I watch Monsieur 's windows . Monsieur O'Hara watches until midnight , and I watch from then until day . '' `` Oh , I know that , '' said the other . `` I 've seen you more than once in the moonlight , but to-night , mon vieux , slumber will overcome you . Exhaustion will have its way and you will sleep .