The next morning, Dr. Sheppard realizes that, due to the “exhilaration” of having a perfect Mah Jong hand, he’s been indiscrete about sharing information. He goes to the funeral of Mrs. Ferrars and Roger Ackroyd, afraid that Poirot will reproach him for spreading information. At the funeral, Poirot doesn’t reproach him, but only asks for his help examining a witness: Parker. Poirot is now fairly sure that Parker was Mrs. Ferrars’s blackmailer—or at least, he tells Sheppard, “I hope it was he.”
Poirot’s cryptic remark might suggest that he has another theory for who the blackmailer could be, and is worried that this second theory might turn out to be the truth. The fact that he feels invested in someone not being guilty is an early indication that he might already be considering his “friend” Sheppard with suspicion.
At Fernly, Poirot and Dr. Sheppard greet Parker. Poirot asks Parker if he’s ever blackmailed someone, and Parker becomes very offended. Poirot demands to know who Parker’s last master was, and Parker says, “a Major Ellerby.” Immediately, Poirot explains that he knows Major Ellerby to have been a drug addict and potential murderer. Poirot calmly explains that Parker blackmailed Ellerby, and still receives a “good sum” to keep quiet about the murder. Parker admits that Poirot is right—but he insists that he didn’t murder Roger Ackroyd. He says he listened to Ackroyd on the night of the murder, and after listening, Parker thought that he could get “a share of the package” by blackmailing Roger. Poirot asks to see Parker’s finances, and Parker obliges. He shows Poirot that he’s invested money, much of it from blackmailing Major Ellerby, in National Savings Certificates. Poirot then dismisses Parker.
Poirot claims to have known all about Major Ellerby (though there’s no explanation for how, exactly, he knows this is offered—maybe Poirot knows him from a previous case, or maybe he’s been investigating this matter without Sheppard’s knowledge. Parker insists—and Poirot seems to believe—that he didn’t kill Roger Ackroyd, even though he’s blackmailed others. Notice that Parker seems to think that Roger, not Mrs. Ferrars, was the real blackmail target, suggesting that Parker is either lying or doesn’t really know what’s going on between Roger and Mrs. Ferrars (and thus is probably innocent of murder). Notice that Poirot isn’t interested (as the police might be) in judging or persecuting Parker’s other crimes—he’s only focused on solving the puzzle of Roger’s death.
Alone, Poirot tells Dr. Sheppard that he believes Parker: Parker wasn’t the killer, and he sincerely thought that Roger Ackroyd, not Mrs. Ferrars, was the blackmail victim. Dr. Sheppard nods, and then admits to Poirot that he told his sister and guests about the ring in the goldfish pond. Poirot laughs and says that Sheppard can do whatever he wants. Their next task, he now explains, is to visit Mr. Hammond.
Poirot seems oddly un-phased that Dr. Sheppard revealed the sensitive information about the golden ring in the pond—possibly suggesting that Poirot hasn’t shared any truly crucial information with Sheppard.
Dr. Sheppard and Poirot visit Mr. Hammond to inquire about Mrs. Ferrars. Sheppard recaps his conversation with Roger Ackroyd on Friday, and Hammond is unsurprised to hear that Mrs. Ferrars was being blackmailed—he’d suspected as much for a while, since Mrs. Ferrars was losing money. After Hammond leaves, Poirot tells Sheppard he’s sure of Parker’s innocence—there’s no way he would have continued on as a butler if he’d gotten so much money from Mrs. Ferrars. Poirot also raises the possibility that Roger threw the letter in the fire after reading it.
Parker now has a pretty solid alibi for not killing Roger: the fact that he’s still a butler. No butler who’d been so successful at blackmailing someone as rich as Mrs. Ferrars would continue to be a butler for very long. Poirot also notes that the absence of the letter doesn’t necessarily prove that the killer knew about the blackmail, even if it seemed to do so at first.
Dr. Sheppard invites Poirot to his home. There, Caroline asks Poirot if he’s found Ralph Paton in Cranchester. Poirot is surprised for a moment, but then explains that he only visited Cranchester to see the dentist. Caroline goes on to tell Poirot, very excitedly, that she believes Flora to have killed Roger Ackroyd. Parker never heard Roger say goodnight—suggesting Flora killed him and then told Parker not to enter the study. Speaking almost to himself, Poirot says, “Let us take a man—a very ordinary man.” This man, Poirot explains, is not a killer, but he has a trace of weakness. He’s in some difficulty, and he’s stumbled upon a valuable secret. The secret corrupts him. Eventually, he faces exposure for his sins—desperate to maintain his reputation, he lashes out, and “the dagger strikes.” Caroline says, “You are speaking of Ralph Paton,” but faults Poirot for criticizing “a man unheard.”
In retrospect, this is one of the first points in the novel when Poirot is shown to believe that Dr. Sheppard is the murderer. He’s shown signs of distrust for Sheppard before, but now he fully indicates that he’s been considering whether Sheppard is capable of killing someone. Caroline believes that Poirot is talking about Ralph Paton, when he’s really talking about Dr. Sheppard himself: an ordinary yet weak man who, in order to save his reputation and recover from some financial difficulties (the bad investments Sheppard has twice mentioned) commits a horrible crime.
Just then, the phone rings, and Dr. Sheppard answers it: the police have detained a man, Charles Kent, in Liverpool. He’s believed to be the stranger who was at the Ackroyd house on the night of the murder.
The chapter ends on something of a cliffhanger: now that the stranger has been apprehended, there may be new insight (or new complications) for the case.