Has the BBC drama changed the ending of Agatha Christie's The Pale Horse?

What remains the same in the novel and TV show?

In the original story and in the TV show, Zachary Osborne is the killer. And people are not dying by magic, but by thallium poisoning.

Clients thought they were hiring a trio of witches to bump off their elderly relatives or rivals with their special powers, but they were actually hiring Osborne – who posed as a workman and subtly poisoned their victims so they died of seemingly-natural causes like heart attacks. The mystery was solved and the killing spree came to an end.

How has the ending been changed from Agatha Christie's novel?

In the novel, Mark Easterbrook and his friend (later fiancée) Ginger are determined to get to the bottom of things, so they come up with a scheme. Mark poses as a potential client for The Pale Horse, and is given an appointment with a shady ex-lawyer who is the go-between. He makes up a story that he wants to get his first wife bumped off, because she's just resurfaced and threatened to derail his upcoming engagement with Hermia. Meanwhile, Ginger plays the part of his first wife, who did actually once exist but conveniently died ages ago abroad.

Mark is then summoned to see the witches, and they put on a show that leaves him pretty shaken and torn between the rational and the irrational. Worryingly, Ginger also begins to get very ill. Have the witches actually used their magic powers to curse her? Is it all true??

No, as it turns out. Mark suddenly puts everything together and realises it's all down to thallium poisoning! Someone has been working with the witches and doing the dirty work of the actual killings, and whoever it was has got to Ginger somehow. Thallium causes a wide range of symptoms and deaths can look like natural causes, but all the victims' hair had been falling out, which provides the clue. The witches were just a smokescreen.

Suspicion initially falls on Oscar Venables, a wealthy Much Deeping resident with inexplicable amounts of money. And Zachary Osborne, the seemingly-trustworthy pharmacist, insists he witnessed Mr Venables following Catholic priest Father Gorman just before his murder. But there's one big problem: Venables is in a wheelchair after suffering from polio, and could not have been walking the London streets. Inspector Lejeune is stumped.

But not for long! Because he soon realises that the killer is none other than Zachary Osborne himself.

Osborne worked with the witches to convince clients they were killing people using magic, but the truth was more prosaic. He employed women (like Jessie Davis) who thought they were working for a legitimate company, and sent them into the victims' homes to carry out consumer surveys; while they were there, they unknowingly collected the information he needed. Osborne himself then delivered the poison by pretending to a workman, gaining access to the victims' houses, and then tampering with their favourite face creams or foods to add deadly poison.

Osborne had chosen Venables as a plausible scapegoat and tried to frame him, but he hadn't realised about the wheelchair – a crucial mistake. In the end, Ginger recognised Osborne as the man who'd come to read the gas meter. Lejeune staged a scene (with Mark Easterbrook looking on) and Osborne was outed as the killer.

How does BBC drama The Pale Horse end? Here's the explanation...

In the TV drama, Zachary Osborne (Bertie Carvel) has been running an unlikely scheme. He's essentially been killing-to-order, removing "obstacles" from people's lives using poison and accepting payment anonymously via banker's draft. And the clients don't find him or even know who he is; he finds them. Osborne identifies people with potential (evil stepmothers, greedy heirs, and so forth); he then contacts them via letter and waits for them to write back if they're keen to see someone dead.

That's when the witches come in handy. Mr Osborne sends his clients to visit the trio at The Pale Horse to have their fortunes told, and so his clients think they're actually using the services of the three witches. The clients then believe that these unexplained deaths are brought about via *magic*, which is a lot more palatable and hands-off as a way of getting someone to die. It's also not particularly illegal to try to kill someone with so-called magic, ever since laws against witchcraft were repealed way back in 1735 (fun fact!).

What the clients don't know is that, in reality, the killings are carried out by thallium poisoning. Osborne poses as a workman, visits the victims at home, and plants the poison or slips it into their water supply or food. This is very much illegal. It also makes the deaths look like they're from natural causes, and no suspicions are aroused.

In this version of the story, the witches are not involved in the killings. They don't know that Mr Osborne has been using them as part of his scheme. But they have noticed a trend: people keep coming to see them to ask for fortunes to be told, and the people they mention keep dying. The witches read the obituaries and wonder what's going on.

One of the witches' repeat clients is Mr Osborne's helper Jessie Davis (Madeleine Bowyer). The witches twig that she knows something about what's really going on, and give her a good fright that pushes her to do the right thing. Osborne realises she's wavering and poisons her too, but just before she dies she writes a list of names and slips it into her shoe – a list which is inconveniently found by the police.

And why was Mark Easterbrook (Rufus Sewell) on the list? Because of a misunderstanding!

His first wife Delphine (Georgina Campbell) had been to see the witches entirely of her own accord, because she genuinely wanted to get her newlywed husband's fortune told. But the witches wondered whether her visit meant this man called "Mark Easterbrook" was going to be the next victim, so they mentioned his name to Jessie – and she wrote it on her list with a question mark, wondering if Osborne had taken on a new client without telling her. (He hadn't.)

When Zachary Osborne realised that this Mark Easterbrook bloke thought he might be next (and when DI Stanley Lejeune agreed), he decided to make it come true and make Mark believe in the whole thing.

Osborne posed as another potential victim; he made creepy matching corn dollies for them both; he started to poison Mark so his hair came out in clumps. The scheme even extended to killing Lejeune (Sean Pertwee) and trying to kill second wife Hermia (Kaya Scodelario), knowing that Mark wanted both of them dead (and had asked the witches to remove these "obstacles"). But ultimately, the plan was to stop playing with Mark and kill him too – once he'd had enough punishment for his evil ways.

And in this telling of the story, Mark definitely has some evil ways. He killed his first wife in a jealous fit, knocking the radio into the bath and electrocuting her; he covered it up; he indirectly murdered Lejeune; he cheated on, emotionally abused and gaslit his second wife Hermia, and then had her poisoned and put into a coma. Not great stuff.

But Mark does finally work out the truth and put the pieces together: Zachary Osborne is not a potential victim, but is actually a twisted killer. Mark realises: this man had seemed to know about the death of Thomasina Tuckerton BEFORE her body was found! In the final showdown, Mark kills Osborne and set his workshop on fire.

Is Mark Easterbrook dead? What does the TV show ending mean?

Look, we can't 100% say. Unless we're missing something, the ending is deliberately ambiguous. Sorry!

But let's talk about what we do know...

In the final moments of the episode, we see Mark Easterbrook pick up the newspaper from his doormat and enter his flat. Alongside a picture of him, the headline is, "Mystery death of antique dealer, Easterbrook tragedy strikes again" – and he looks up to finds himself trapped back in the past (or in a nightmarish vision), as Delphine picks up the radio and heads for the bathroom. Then electricity fuses and the lights go out. "Not again. Please – not again," he begs.

Perhaps Mark has been killed by the thallium poisoning, after all; even though he killed Osborne, perhaps he was too late to save himself. Perhaps this is just his personal hell in the afterlife.

Or, perhaps, the witches have killed him and/or trapped him in a perpetual nightmare. There's some hint of this earlier in the episode:

"That's that," says Sybil (Kathy Kiera Clarke) as Mark leaves the Pale Horse.

"Nearly," responds Thryza (Sheila Atim). Clearly, they have something extra in store for him.

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It's also significant that, just before Mark walks into the flat and reads of his own death, Hermia Easterbrook has just suddenly (almost miraculously) woken up in hospital. She sees the three witches by her bedside, and they explain some things to her, but it's not clear whether the witches physically visited the hospital at all or if this is some form of vision or magic.

Have the witches switched their fates – saving Hermia and dooming Mark?

You may have to make up your own mind...

The Pale Horse is available on BBC iPlayer now