When a man and his son return home they notice some shards of glass on their doormat. A glass panel had been knocked out of the door. They enter the house to discover an intruder. The man sends his son to get the police and then he tackles the intruder as he is only a small man. However, the small intruder had a gun and kills the householder. Scotland yard begin their investigation by knocking on doors locally to discover a small man had been casing joints by knocking on doors under a false pretence.