eleven o'clock
`` Are you sure ? '' he sharply demanded , while in spite of his long and severe training , he turned very white , and his under lip twitched nervously . `` Certainly , or I should not have so stated , '' returned the clerk , with some dignity . `` When young Mr. Walton settled his bill , he ordered a carriage to be in waiting at eleven o'clock , and both he and his mother left the house at that time . I regret your disappointment , sir , in missing them . '' This was almost more than Mr. Rider could bear ; but he could not doubt the man 's word , and he feared the thieves had escaped him again . They must have left while Mona was telling him her story at the detective headquarters .