Who is the killer in The ABC Murders? 5 key theories after episode 2

Whodunnit and whydunnit? Ahead of the final episode, here are five suggestions about who the ABC murderer could be...

Eamon Farren as Cust in The ABC Murders

Alice Asher, Betty Barnard, Carmichael Clarke, Benny Gru: the bodies are piling up and both Hercule Poirot (John Malkovich) and Inspector Crome (Rupert Grint) are desperate to solve the case of the ABC murders.


Ahead of the final episode of the Agatha Christie murder mystery, we’ve collected together five theories about what could really be going on…

Theory 1: Is Cust actually the murderer?

Cust in The ABC Murders

Things are not looking great for Alexander Bonaparte Cust. We’re a bit sceptical about the idea of Cust as the real killer, but you have to admit: every time there’s a murder, he’s right there nearby with his suitcase full of stockings. That’s surely no coincidence.

After his appearances in Andover and Bexhill, Cust can be seen in Churston on 10th April, sinisterly eating a sandwich and watching unobserved as Sir Carmichael Clarke’s recently-fired secretary Thora Grey smokes a cigarette. In fact, he later manages to sell Thora a pair of stockings. That evening, Sir Carmichael goes out to walk his dog and is killed with a garden shovel.

And do we see him at Doncaster? Of course we do.

There’s Cust again, selling stockings outside the theatre where Dexter Dooley the ventriloquist is about to perform. Presumably, the alliterative Dexter Dooley is the intended victim of ABC’s next murder, although it is not Mr Dooley who dies; instead, the man sharing his dressing room – an unlucky comic named Benny Gru – takes his place as murder victim number four.

Cust’s clothes count against him, too. Whoever has been sending the Belgian detective all these scary letters clearly has a weird obsession with him, and multiple people have noticed that Cust dresses just like Poirot himself. Lady Hermione says she initially thought the stocking salesman she saw from her window was Poirot arriving for a visit, and Megan Barnard suddenly recalls: “There was a man at the Palais with the same clothes as you.” That man was Mr Cust.

As the murders progress, Cust is also increasingly suffering from an illness causing seizures and blackouts. He tells Lily that he doesn’t want to be a monster, and it certainly seems like he either knows he’s the murderer – or suspects that he could be killing these men and women during the times he doesn’t remember.

(Also, as a side note – and not to kink-shame or say his sexual interests have ANY bearing on whether he’s a serial killer or not – but MY GOSH that scene 35 minutes in when Lily climbs on Cust’s back and puts her heel RIGHT into the bloody open wound and presses down? OUCH. Almost as stomach-churning as the scene with Mr Treadgold and his pussy lump and the runny fried egg…  thanks for that, Sarah Phelps.)

Theory 2: Has Cust been set up?

Rupert Grint in The ABC Murders

Almost everything points towards Cust as our killer, although Hercule Poirot and Inspector Crome have yet to identify or catch him. But isn’t this just too convenient? What if Cust has been set up to take the fall?

Although Cust has the typewriter, it’s not clear whether it’s his fingers that tapped the keys that wrote the ABC letters. If anything, our Mr Cust seems too fearful and shy to kill anybody – he’s more comfortable following instructions rather than creating murderous masterplans. And if he were the serial killer, he would surely revel in the media coverage? Instead, it seems to make him nervous.

It’s possible that someone (as yet unknown) is trying very hard to frame Cust as the killer. But who? And how? And why?

Theory 3: Are Franklin Clarke and Thora Grey involved?

Franklin Clarke and Thora Grey in The ABC Murders

Of the four murders we’ve had so far, it is C for Clarke which has stood out as most interesting.

Poirot first visited Sir Carmichael Clarke’s family in 1928 when he was at the peak of his fame. Back then, he had a nice little side-earner hosting murder mystery parties for the rich, and so Sir Carmichael hired his services for his wife Lady Hermione Clarke’s birthday party. She was star-struck.

Now, Lady Hermione is dying from some kind of horrible cancer in the throat and she’s coughing up blood all over the place and her loving husband is utterly distraught. Sir Carmichael’s pretty young secretary Thora Grey has her eyes on the prize and is keen to become her boss’s second wife, but she misreads the situation; when she kisses him, he fires her on the spot.

What’s a girl to do? Perhaps, shift her attentions onto her boss’s younger brother, Franklin, who is next in line to inherit the estate once both Lady Hermione and Sir Carmichael are dead. The former is already on her deathbed and the latter is just about to meet an untimely demise at the sharp end of a garden shovel.

So could Thora be involved in Sir Carmichael’s murder? Or could his seemingly-devoted brother Franklin? Perhaps. After all, Poirot has suggested that the killer could be a woman, or that the letters were written by a woman pretending to be a man (or, indeed, a man pretending to be a woman).

But although Thora’s clearly a slippery character, it’s unclear why she would get involved with any of the other murders. The same applies to Franklin, who actually goes so far as to hire Poirot as a private detective because Inspector Crome is so clueless. Both of them could benefit by Sir Carmichael’s death (particularly if a romance blossoms between them), but they gain nothing from the deaths of Alice Asher, Betty Barnard, or the unfortunate Benny Gru.

Still – it remains a possibility that Thora, or Franklin, or Thora and Franklin are more deeply involved than they’d care to admit.

Theory 4: Is the killer someone from Poirot’s past?


“There is a code. The code is me.” That’s what Hercule Poirot tells Inspector Crome when they have their détente and begin to solve the case of the ABC murders together.

Poirot has noticed an alarming pattern to the murders. Not only is ABC sending him those sinister letters (“chin-chin!”), but every single death has been connected to a place or person from his own past.

In 1921, he had a cream tea at the Ginger Cat in Bexhill, where Betty Barnard would work more than a decade later. The menu he signed has been framed and kept on the wall.

In 1928, he attended Lady Hermione’s birthday party in Churston, where he also met Thora, Carmichael, and Franklin.

And for Andover, the connection is so obscure that he had no idea until he saw the framed newspaper clipping in the back room of Mrs Asher’s shop: “Local lady’s gift for surprise baby.” In 1914, a train carrying refugees was delayed at the sidings, and one of the passengers gave birth to a little boy – who was provided with clothing by the generous Alice Asher. The man who delivered the child was none other than M. Hercule Poirot, who had no idea he was anywhere near Andover.

“The killer knows me, knows all about me… they know everything. And the next locale, the letter D, will also be a place I have visited,” he tells Crome. Sure enough, the next place on the list is Doncaster.

As played by John Malkovich, Poirot is a troubled man with many secrets. He is deeply religious, but has a difficult relationship with God and refuses to confess or to take the sacrament because he feels he does not deserve forgiveness. Repeatedly, he experiences flashbacks to trauma he experienced during the war and the invasion: a close-up of a terrified young man’s face, scared people sheltering in a church and frantically praying. It’s also not even clear whether he was a policeman at all before the war.

The ABC murderer’s personal knowledge of Poirot’s life from the moment he arrived in England must surely force him to consider whether he knows this man (or woman) from somewhere. Did he meet this person in a past life in Belgium? Were they involved in this trauma of his? Or (as Crome suggests) could the killer be the boy who was delivered on the refugee train in 1914? It’s a mystery.

Theory 5: Is the ABC murderer a total stranger?

The ABC Murders

Mes enfants, we have to consider one final theory: that the ABC killer is a complete and utter stranger.

After all, any person anywhere in the country could come up with this scheme to travel the railway network and send letters to Poirot and murder people alphabetically. Sure, they’d need to do a lot of research into Poirot, and they’d need to do a lot of planning. But what if the murderer is an anonymous psychopathic serial killer – instead of any of the characters we’ve met so far?

It would be a bold move. But you never know…


This article was originally published in December 2018

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