Elspeth McGillicuddy has come down from Scotland to visit her old friend, Jane Marple. On the way, she sees a woman strangled in a passing train. Only Miss Marple believes her story, as there is no evidence of wrongdoing. The first task is to ascertain where the body could have been hidden. Comparison of the facts of the murder with the train timetable and the local geography lead to the grounds of Rutherford Hall as the only possible location; it is shielded from the surrounding community, the railroad abuts the grounds and so on. Miss Marple calls upon an acquaintance, Lucy Eyelesbarrow, who is a professional housekeeper renowned for her efficiency and organizational skills. Lucy agrees to take a position at Rutherford Hall, and the hunt is on.
Rutherford Hall was built by Josiah Crackenthorpe, purveyor of tea biscuits. His son, Luther, now a semi-invalid widower, had displayed spendthrift qualities in his youth. To preserve the family fortune, Josiah's will provided Luther with a home and income for life but otherwise left everything in trust for the grandchildren. They share equally in the estate, but only if they live long enough to inherit it.
Two of Luther Crackenthorpe's children, Edmund and Edith, died during World War II. The remaining heirs to the estate are Cedric, a painter and lover of women who lives on Ibiza; Harold, a cold and stuffy banker with a hidden passion for the ballet; Alfred, the black sheep of the family and a man known to engage in shady business dealings; and Emma Crackenthorpe, a spinster who lives at home and takes care of Luther. At the time of the story the brothers are visiting for Christmas, as are Edith's surviving husband, Brian Eastley, and their son Alexander, along with his friend, James Stoddart-West. A frequent visitor to Rutherford Hall is Dr. John Quimper, who looks after Luther's health and is quietly romantically involved with Emma.
Lucy uses golf practice as an excuse to search the grounds. She eventually finds the woman's body hidden in a sarcophagus in the old stables, amongst Luther's collection of dubious antiques. But who is she?
The police identify the victim's clothing as being of French manufacture. Emma reveals that she has received a letter from a Frenchwoman named Martine, who claims to have been married to Edmund just before his death in the War. The letter explains that Martine was pregnant when Edmund died, and that she now wishes their son to have all of the advantages to which his parentage should entitle him. The police conclude that the body in the sarcophagus is Martine, but this struck down by Lady Stoddart-West, James' mother. She, it seems, is Martine!
The plot thickens when Lucy's curry proves to be laced with arsenic. The whole family takes ill, and Alfred dies. Sometime later, after returning home to London, Harold receives a delivery of some tablets that appear to be the same as the sleeping pills prescribed to him by Dr. Quimper. They prove to be poisoned, and Harold dies. One by one, the heirs to Josiah's fortune are vanishing.
Lucy arranges another tea time visit to Crackenthorpe Hall for Miss Marple, and Mrs. McGillicuddy is invited down from Scotland. She is instructed to ask to use the lavatory as soon as they arrive, but is not told why.
Miss Marple is eating a fish sandwich when she begins to choke. It seems she has a fish bone stuck in her throat. Dr. Quimper moves to assist her. Mrs. McGillicuddy enters the room, sees the doctor's hands at Miss Marple's throat, and cries out, "But that's him! That's the man on the train!" Miss Marple had deduced that the strange angle and poor lighting conditions on the train had caused Mrs. McGillicuddy to give an inaccurate description of the murderer's height and hair color, but correctly concludes that her friend would recognize the real murderer if she saw him again in a similar pose.
It transpires that the murdered woman had been married to Dr. Quimper many years before. They had separated but she was Catholic and would not agree to a divorce. He murdered her so he would be free to marry Emma and inherit Josiah's fortune once he had gotten rid of the other heirs.
This book has Miss Marple give voice to Agatha Christie's view on the death penalty when she remarks, "I am really very, very sorry that they have abolished capital punishment because I do feel that if there is anyone who ought to hang, it’s Dr. Quimper." Capital punishment in Britain was not finally abolished until 1969 (1973 for Northern Ireland), but there were many periods when the death penalty was temporarily suspended by the Government while Acts of Parliament for abolition were pending. One of these "temporary abolitions" happened in February 1956 but ended in July 1957. So, the death penalty had been in moratorium when Christie wrote 4.50 From Paddington but was reinstated about the time the book came out.
The novel was reviewed in The Times edition of December 5, 1957 when it stated, "Mrs Christie's latest is a model detective story; one keeps turning back to verify clues, and not one is irrelevant or unfair." The review concluded, "Perhaps there is a corpse or two too many, but there is never a dull moment.
Fellow crime writer Anthony Berkeley, writing under the nom-de-plume of Francis Iles, reviewed the novel in the December 6, 1957 issue of The Guardian when he confessed to being disappointed with the work: "I have only pity for those poor souls who cannot enjoy the sprightly stories of Agatha Christie; but though sprightliness is not the least of this remarkable writer's qualities, there is another that we look for in her, and that is detection: genuine, steady, logical detection, taking us step by step nearer to the heart of the mystery. Unfortunately it is that quality that is missing in 4.50 from Paddington. The police never seem to find out a single thing, and even Miss Marples (sic) lies low and say nuffin' to the point until the final dramatic exposure. There is the usual small gallery of interesting and perfectly credible characters and nothing could be easier to read. But please, Mrs Christie, a little more of that incomparable detection next time.
Robert Barnard: "Another locomotive one – murder seen as two trains pass each other in the same direction. Later settles down into a good old family murder. Contains one of Christie's few sympathetic women. Miss Marple apparently solves the crime by divine guidance, for there is very little in the way of clues or logical deduction.
The book was made into a 1962 movie starring starring Margaret Rutherford in the first of her four appearances as Miss Marple.
The BBC stuck very closely to the original plot with its 1987 version, starring Joan Hickson, who had appeared in the Rutherford film as Mrs. Kidder. Departures from the original story include the absence of any food poisoning. Alfred is still alive at the end, though suffering from a terminal illness that Dr. Quimper apparently misdiagnosed deliberately. As in the earlier film version, Harold is murdered in what appears to be a hunting accident. The other major departure is at the end, where Miss Marple unambiguously opines that Lucy Eyelesbarrow will marry Bryan Eastley, a possibility that is only hinted at in the novel.
Another version was made by ITV in 2004 starring Geraldine McEwan as Miss Marple and a cast that included David Warner, Griff Rhys Jones, Ben Daniels and Pam Ferris. It has been shown in the United States under the title What Mrs. McGillicuddy Saw. It deviates from the original by making the character of Dr. Quimper far more sympathetic, even though he is still a murderer. There is no mention of his being cold-blooded, as there is in the earlier film version, and Miss Marple does not comment, as she does in the novel, that if there is one person who ought to be hanged, it is Quimper.
In the UK the novel was first serialised in the weekly magazine John Bull in five abridged instalments from October 5 (Volume 102, Number 2675) to November 2, 1957 (Volume 102, Number 2679) with illustrations by K. J. Petts.
The novel was first serialised in the US in the Chicago Tribune in thirty-six instalments from Sunday, October 27 to Saturday, December 7, 1957 under title Eyewitness to Death.
An abridged version of the novel was also published in the December 28, 1957 issue of the Star Weekly Complete Novel, a Toronto newspaper supplement, under the title Eye Witness to Death with a cover illustration by Maxine McCaffrey.