ten minutes past ten
`` I shall always be grateful to you , '' he declared . `` Do n't be too sure of that , '' she answered enigmatically . _ Chapter XXIII _ At exactly ten minutes past ten Annabel rang the bell of her sister 's flat . There was no response . She rang again with the same result . Then , as she was in the act of turning reluctantly away , she noticed a thin crack between the door and the frame .