about eleven o'clock
That afternoon when Mona went down to dinner , the clerk of the hotel waylaid her and quietly slipped an envelope into her hand . `` Thank you , '' she said , in a low tone , and hastily concealed it in her pocket . When she was alone again she broke it open and read , with almost as much disappointment as the detective himself had experienced , when he found that his birds had flown , these words : `` Gone ! They gave us the slip about eleven o'clock . Save the scrap of cloth -- it may be needed later . R. '' `` Oh , dear ! '' sighed Mona , regretfully ; `` and the Palmer robbery is still as much of a mystery as ever . ''