A.B.C. plan

The A.B.C. plan is the alphabetical murder scheme devised by Franklin Clarke to hide the murder of his brother, Sir Carmichael Clarke, inside an apparent series of unrelated killings. Its letters, railway guide, and escalating sequence of places give the crimes a conspicuous pattern, while also directing suspicion toward Alexander Bonaparte Cust, whom Clarke has prepared as a substitute culprit.

Design and apparent pattern

The plan presents each crime as a step in an alphabetical progression: the victims and their locations begin with successive letters. The A.B.C. railway guide reinforces the pattern, and advance-warning letters signed A B C announce where the next killing is to occur. In the fourth letter, the writer taunts Hercule Poirot and the police, invokes the refrain about trying again, and announces that the next incident will take place at Doncaster on September 11. The correspondence thus turns the sequence into a public challenge as well as a device for directing the investigation.

The apparent logic of the series conceals a mismatch. The victims differ widely, and Poirot finds no consistent sex or age preference that would explain their selection as the work of a conventional killer. The alphabetical rule imposes order on crimes whose victim choices otherwise appear haphazard. Poirot reads that tension as a clue: the pattern is important to the murderer, but it does not arise from a stable category of victims. The choice of a railway guide also suggests a railway-minded, boyish sensibility, a suggestion reinforced by the schoolboy-like tone of the letters.

Cust as the intended suspect

Clarke builds the plan around Cust’s initials and the circumstances that make him seem useful as a tool. Cust’s elaborate Christian names, his account of epileptic seizures and headaches, and his shrinking, insignificant personality strike Clarke as suitable for the role. The initial C also connects Cust to Clarke’s brother and to Churston, giving Clarke the nucleus from which to construct the alphabetical scheme. Clarke even hints to Cust at the possibility of his own death, though he cannot expect how powerfully that suggestion will affect him.

The impersonation is prepared materially as well as psychologically. Clarke orders a large consignment of hosiery in Cust’s name, sends A B C guides made to look like part of the same parcel, and types a fictitious employment offer that promises a salary and commission. He then gives Cust the typewriter used to produce the later letters. These arrangements make the correspondence and the apparent connection between Cust and the crimes look consistent, while concealing Clarke’s authorship of the scheme.

The crimes and the concealed motive

The alphabetical design requires Clarke to find victims whose names and home towns match the early letters. For the B stage, he varies his approach: rather than rely on a warning that might reach a shopkeeper, he frequents cafés and tea-shops, looking for a suitable woman with the right initial. He chooses Betty Barnard, takes her out once or twice, and explains that, because he is married, their meetings must be discreet. Her apparent connection to a sequence of alphabetical murders helps disguise the personal access that makes her a target.

With these preparations in place, Clarke sends Cust the Andover list and directs him to go there on a particular date. He also sends Poirot the first A B C letter. Clarke then goes to Andover and kills Alice Ascher; the first murder succeeds without an event that disrupts his plan. The staged pattern is therefore not merely a theory imposed after the crimes: Clarke constructs it in advance, using Cust’s movements and the letters to frame the killings as a serial campaign.

The deeper motive is separate from the public pattern. Clarke resents his brother’s wealth and sees the possibility of children as a threat to his chance of inheriting it. His meeting with Cust supplies the means to make the murder of Sir Carmichael appear to belong to the same alphabetical series as the earlier deaths. The C of Cust’s initials, Sir Carmichael’s name, and Churston together give the plan its central alignment; the spectacle of a serial killer is a fabricated defence against the obvious questions of opportunity and inheritance.

Exposure and significance

The plan depends on Clarke’s belief that each successful crime confirms his cleverness. Poirot describes the criminal as a gambler who mistakes luck for ability and cannot tell when to stop: after repeated success, the run turns. For Poirot, the clue of the stockings marks the beginning of that reversal. The apparent neatness of Clarke’s design makes him more, not less, vulnerable to the small failures that expose how the pattern was manufactured.

Poirot’s reconstruction reverses the case’s central assumption. The crimes do not prove that Cust is a resourceful serial murderer; the sequence is a screen created by a calculating man who is prominent in one of the crimes and needs to obscure a direct motive. The A.B.C. plan is therefore both a method of concealment and a narrative trap: its orderly letters invite the police to see one kind of killer, while the differences among the victims and the practical arrangements behind the correspondence point toward another.