we didn't have any servants. He also put in that air- vent on the wall between his room and this one.'Holmes pulled the rope. 'But it doesn't work,' he said. 'How strange! And it's just over the air-vent. That also is interesting. Why have an air-vent on an inside wall? Air-vents are usually on outside walls.'Then we went into Dr Roylott's room. Holmes saw a large metal box near the wall.'My stepfather keeps business papers in there,' said Helen.'Does he keep a cat in there too?' asked Holmes. 'Look!' There was some milk on a plate on top of the