midnight
And he pointed out briefly where the five men should be stationed and why , and Shad , somewhat mollified by the cigarette , shrugged and agreed . `` We 'll do sentry duty in the regular way , '' went on Peter cheerfully , `` with a corporal of the guard and a countersign . I 'll explain in detail to-morrow . '' And then to Shad , `` I 'll take command until midnight , when you 'll go on with the other shift until four . I 'll make it clear to the other men . The countersign is the word ` Purple . ' You 'd better go and turn in .