You can’t just put a book on the telly; it’ll fall off. Gravity aside, page-to-screen adaptations demand change. A novel’s worth of characters and sub-plots are too great for two hours of viewing. To work as television, books require careful filleting – screenwriters to sweep their boning knife around the delicious flesh and discard the unappetising pale flab. Sarah Phelps, whose most recent literary adaptation The Pale Horse, has just aired on BBC One, is one of the best boners around. With huge plot spoilers for both, here’s how the Agatha Christie original differs from the TV drama… In the series, Jessie writes the list in her final hours, knowing that Osborne has poisoned her, and plans to take it to the police and confess, but Osborne – a retired chemist in the book, not the owner of a hardware and repairs shop – murders her in the street before she can do so.

Jessie Davis isn’t Osborne’s accomplice in the book

Osborne’s murder methods differ slightly in the book. He uses information gathered by a customer research company (for which Jessie Davis works) to ascertain which household and pharmaceutical products his victims use, and then enters their home under a handyman pretext and swaps their product for one laced with Thallium. In the TV series, he puts the Thallium in their water supply. The book Jessie is at first unaware of the killings her questions help with, but starts to suspect and so is poisoned by Osborne to cover his tracks. In the TV series, she’s working for Osborne and fully aware of what’s going on.

Osborne uses a go-between in the book

In a seedy Birmingham office, disbarred lawyer Mr Bradley receives Osborne’s clients. To weasel his way around the law, he takes bets against the longevity of the ‘obstacle’ in the client’s way. The client places a bet that so-and-so will live until a certain date, and he bets against them at extortionate odds, collecting the winnings when the ‘obstacle’ fails to remain alive. In the series, Osborne contacts the clients directly by post, going through the papers to get the names and writing to offer to rid them of their ‘obstacle’, sending them to The Pale Horse to ask for the fortune of the person they want killed. In the series, Mark is cheating on his second wife Hermia with Tommy and when he wakes up next to her dead body, he does nothing to alert the authorities and sneaks out, leaving her to be discovered days later.

Mark’s first wife wasn’t electrocuted

In the book, Mark’s first wife Delphine is Doreen. Infatuated with her prettiness, they married secretly (the family wouldn’t have approved) while he was still very young and at university. Travelling in Italy, Mark discovered Doreen was having an affair with another man, with whom she was killed in a car accident. It’s worth noting that we have only Mark’s word for this series of events in the book, so Phelps’ idea that he killed his first wife in an unwarranted jealous, possessive rage is a neat dramatic extraction.

Mark, Ardingly and Osborne’s names aren’t on the list

In the book, the names on the list are: Ormerod, Sandford, Parkinson, Hesketh-Dubois, Shaw, Harmondsworth, Tuckerton, Corrigan and Delafontaine, the last two with question marks next to them. In the TV series, the list features Mark’s godson David Ardingly, and Osborne, while Mark’s name has the question mark next to it (because Jessie heard the name from the women at The Pale Horse but didn’t know if he was one of Osborne’s clients). In the book, Mark learns about the list through his police surgeon and criminologist friend from university, Corrigan.

Agatha Christie is (sort of) in it

Mark has a friend named Mrs Ariadne Oliver who is a writer of detective mysteries and known in the Christie canon as a self-deprecating avatar for the writer herself. She’s used by Christie to stage conversations pondering murder methods and whether, in this instance, victims could be killed by remote-control magic. Elsewhere in Christie’s work, Ariadne is a friend of Hercule Poirot, and her friends in The Pale Horse – the Calthorps from Much Deeping – are characters who appear in the Miss Marple stories, so think of it as an Agatha Christie Extended Universe if you will. It’s all connected.

Mark isn’t married to Hermia in the book

Book-Hermia is a beautiful, young historian and a theatre-going friend of Mark’s (they go to see a production of Macbeth and in a sly reference to the book’s plot, Hermia complains that the three witches are always awful). He contemplates marrying her, but finds her “damnably dull” and can’t muster the enthusiasm. At one point he pretends to want to marry Hermia as part of a plan to investigate the murders, but merely forgets her by the end, when he marries Ginger, a character who doesn’t appear in the TV series (see below).

There’s another character called Ginger Corrigan

When Mark starts to investigate The Pale Horse, he brings a young art restorer on board named Ginger. She offers to assist him in a plan that involves her pretending to be his first wife, whom he pretends he wants killed by The Pale Horse because she’s stopping him from marrying Hermia – a total fiction. It’s through Ginger – who is visited by a customer researcher before she falls ill and her hair begins to fall out – that Mark works out that it’s Thallium poisoning. At the end, once Osborne is caught, Mark proposes to Ginger and one of The Pale Horse witches predicts that she’ll make a good mother.

There’s no creepy Lammas Fair or corn dollies in the book

But there is a very creepy séance. As part of Mark and Ginger’s plan to pretend to employ the services of The Pale Horse to kill his pretend first wife, he goes to a séance at the former inn. He sees one of the ‘witches’ possessed by a spirit, another sacrifice a white cockerel, and a mysterious box-like machine with electronic dials used. He’s sceptical throughout, unlike in the TV series, when Mark visits The Pale Horse, he really believes he’s under a curse and that the three women can kill remotely.

The book’s ending is happier

In the book, Inspector Lejeune isn’t killed, Osborne is arrested, Mark marries Ginger and (presumably) lives happily ever after. In the TV series, Osborne fatally poisons Lejeune before Mark kills him and sets fire to all the evidence, then Mark is revealed as Delphine’s killer and at least seems to die, ending up trapped in a guilt-ridden vision of her death. Hermia lives though, and presumably inherits Mark’s money and goes on to live a better life out of the bed of a jealous, lying killer. Hooray! Read more about The Pale Horse’s ending here.