midnight
`` Yes , '' said Jimmie , `` but we ai n't . We 're lost in the jungle , if you want to know . '' Ned Nestor and Frank Shaw sat on the porch , that night , for a long time after the other boys were asleep . It had been decided that Frank should stand guard until midnight , but Ned was far too anxious to attempt to sleep . The absence of Jimmie and Peter worried him , and he sat waiting for some sign of their approach until very late . `` Frank , '' he said , after a long silence , `` there has been some talk in this case about your father having an interest in an emerald mine down here . Have you any idea where that mine is ? ''