midday
Old Adelbert agreed to silence . In fact , he repeated after the boy , in English he did not understand , a most blood-curdling oath of secrecy , and made the pirate sign -- which , as every one knows , is a skull and crossbones -- in the air with his forefinger . `` This cave , '' he said , half smiling , `` must be a most momentous matter ! '' Until midday , when the Railway opened for business , the old soldier was free . So the next morning , due precautions having been taken , the two conspirators set off . Three , rather , for Tucker , too , was now of the band of the black flag , having been taken in with due formality a day or two before , and behaving well and bravely during the rather trying rites of initiation . Outside the thicket Bobby hesitated .