Gunfire coming from the home of two elderly, eccentric brothers leads Lanigan to the dead body of the older brother, and the younger brother injured in a fall when he fired a huge revolver at the assailant while precariously balanced on a flight of stairs. The surviving brother lets it slip that one of his nieces came to visit on the night of the murder, leaving her the prime suspect. Everyone suspects that the dead man had a huge fortune stashed somewhere in the house, which the younger brother denies. But when an octagonal box turns up missing, people suspect it was the key to the treasure and the niece is in serious trouble. Lanigan and Rabbi Small, tipped off by the surviving brother's odd behavior, wonder if greed wasn't the primary motive for the murder.