Inspector Mallory can be so sleazy, in this episode he gazes at a window as a lady does a mini striptease. She also happens to be the wife of a decorated policeman Wilber Lesser, whose first wife was found dead some years earlier falling down the stairs.
Agnes Lesser his surviving daughter makes Doll's Houses, dioramas of murder scenes which earns her a commendation. She has invited certain people including Father Brown and Chief inspector Webb, who investigated the original death to a gathering to go through the days of her mother's death. She wants to find the truth, not matter where it leads to. Her father is less than happy about these turn of events.
Webb makes his dislike for Mallory very clear as they have crossed swords in the past. When Webb is found dead, Mallory is arrested for his murder, luckily his peeping Tom act saves him from the gallows.
This is a mystery about hidden childhood trauma, it has a psychological dimension to it which the viewer could probably figure out.