midnight
But try as he might , and tired as he was , sleep refused to visit him , and the harder he tried the wider awake did he become . He also found that he was rapidly becoming obsessed by a horrible feeling that all was not right , that there was some unknown but terrible danger hovering over the sleeping camp . He strove to dispossess his mind of such fancies by assuring himself that sentries were posted everywhere , and that therefore the camp would be early alarmed in the event of an attack being made ; but it was all to no purpose ; the presentiment only held him the more firmly in its embrace . He had just looked at his watch and discovered that it was midnight , and that he had been tossing and tumbling for three hours , when his ears caught a very faint sound , coming apparently from some distance away . Douglas sprang to his feet in a moment , and striding to the flap of his tent , bent all his energies to the task of listening intently . Yes , there it was again ! It was coming from the direction of a wooden suspension bridge which spanned a broad ravine , and which the force had crossed about a quarter of an hour before camping down ; and it took the form of heavy , muffled blows of iron against wood .