All of the suspects had access to the victim (the wealthy patriarch), and the method (eye drops substituted for insulin). Everyone had a potential motive. The actual killer was never seriously considered until the very end, though clues were planted if you knew where to look.
Suspect 7: Laurence, the children’s tutor.
We meet the amateur sleuth and find out he wants to marry the victim's granddaughter.
The victim is murdered and the sleuth is made aware of it.
Amateur sleuth talks to his father, of Scotland Yard, about the case. They agree he is in a unique position to find out who had the most compelling motive. All suspects had access to the method and opportunity. It is a question of who had the greatest motive. The victim was killed when his insulin was replaced with eye drops and he received the wrong injection by his wife. She is the most likely candidate.
Sleuth arrives at the scene. His story goal is repeated: to find out who murdered the victim so he can marry his fiancée. Sophia had no apparent motive, so she is ruled out.
The sons were already financially cared for but would inherit more money. The young widow would be free to remarry.
Sleuth interviews Suspect 2 Phillip, who insists he had no motive.
Magda is overly dramatic but had no apparent motive other than the victim refused to fund one of her plays.
Suspects 4 Roger and 5 Clemency point the finger at Suspect 1 Brenda who they believe was having an affair with Suspect 7 Laurence. Brenda administered the injection and had the strongest motive.
Brenda insists she didn’t notice anything odd about the insulin and gave him the shot as scheduled. She denies having an affair with Suspect 7 Laurence. She felt safe with the Victim, why would she ruin that?
First hint that Suspect 9 Josephine is the killer. Brenda mentions that Josephine isn’t quite right.
Josephine brags that she knows things and always wanted to be a detective. She insists she is more intelligent than the police. She knows the name of the poison and how it was administered. She also states that she did not like the Victim. She points the finger at other suspects. Tells the sleuth Suspects 4 Roger and 5 Clemency were packed to leave town. She overheard a conversation between the Victim and Suspect 4 Roger that suggested Roger was guilty of embezzlement.
Sleuth reveals Suspect 4 Roger’s motive: hide embezzlement from the victim and get money to solve problem. The police confirm that his business was on the rocks. They believe Suspect 4 is too bumbling and it must have been his wife Suspect 5 Clemency.
Thematic statement is made: murder is an amateur crime. Reinforces second clue that Suspect 9 Josephine is the killer, though the sleuth and the police have not seriously considered her.
"Murderers are vain. They think they are far too clever to be caught and want to talk about it."
Sleuth is encouraged to look for people who give false information. They always slip up. He is also admonished to protect the child, suggesting the child could be in danger from the killer because she is always listening at doors and might know something she shouldn’t.
This is a critical chapter. It lays the foundation for Suspect 9’s guilt and dismisses her as a potential suspect in the same paragraph. The Sleuth is told that children sometimes kill on accident but feel horrible when they realize what they have done. This reinforces that children do not kill intentionally, further removing any possibility in the Sleuth’s mind that the child is guilty of premeditated murder.
The Sleuth did not tell the police about the love letters. He interviews Suspect 9 Josephine. She states she lied about the love letters. Reinforces that Josephine is a snoop. The letters play a critical role later.