nine o'clock
The ladder was carried around the building . As the boys looked up they saw all the windows were in darkness save one . That one was in the top row , and was the third from the end . `` It 's against the rules for any of the patients to have a light in their rooms after nine o'clock , '' remarked Frank . `` I wonder what that means ? '' `` Perhaps your father placed it there for a signal , '' suggested Fenn . `` I 'm going to see ! ''