Emily Inglethorp’s murder is the central death in the Styles case and the event around which its competing clues, legal suspicions, and family interests turn. Its solution depends on distinguishing the poison from the medicine that carried it, and on recognizing how a narcotic delayed its effects: Emily died after taking a final dose of her tonic, where strychnine had settled in concentrated form. The investigation’s last turn exposes Alfred Inglethorp as the murderer, while explaining why Mary Cavendish’s conduct and the household’s other encounters with strychnine had pointed attention in misleading directions.

Poisoning and the medical evidence

The post-mortem established strychnine poisoning as the cause of Emily’s death. The amount recovered indicated that she had taken at least three-quarters of a grain, and probably one grain or slightly more. The medical evidence considered accidental ingestion very unlikely: strychnine was not an ordinary domestic poison, and its sale was restricted. These findings made both the quantity and route of administration central questions, rather than allowing the death to be explained as a household mishap.

The timing initially complicated the case. Strychnine’s symptoms generally appeared within one to two hours, while Emily’s after-dinner coffee was taken at about eight in the evening and her symptoms did not emerge until the early hours. That interval seemed to count against the coffee as the source, absent conditions that would retard the poison’s action. The cocoa she habitually drank in the middle of the night was also tested: Dr. Bauerstein’s analysis of the remaining sample found no strychnine. The two familiar drinks therefore left the investigators with a mismatch between the known poison and the observed timetable.

The hidden route and delayed effect

Poirot’s reconstruction supplied a third medium: Emily’s medicine. The poison was already in the prescribed mixture rather than newly introduced into a drink. An extract from a dispensing book described a strychnine mixture in which the salt could, over several hours, precipitate as insoluble bromide crystals. In a cited case, the precipitate collected at the bottom of the bottle, so that the last dose contained nearly all the strychnine. Poirot connected that pharmaceutical process to the empty box of bromide powders found in the case: adding one or two powders to a full bottle could produce the same sedimentation.

The handling of the bottle mattered as much as its contents. The person who usually poured Emily’s medicine was careful not to shake it, leaving the sediment at the bottom undisturbed. That practice allowed the poison to accumulate in the portion eventually taken as the fatal dose. Poirot’s account thus turned an apparently ordinary medicine bottle into the mechanism of the murder, with the sequence of mixing, settling, and dosing explaining how a lethal quantity could be delivered without strychnine being detected in the cocoa or consumed in the coffee.

A separate narcotic accounted for the delayed symptoms. Mary Cavendish had administered a safe but effective narcotic to Emily and Cynthia. The earlier analysis associated with Dr. Bauerstein had asked whether strychnine was present; it had not tested the cocoa for a narcotic, as Poirot’s later analysis did. In his explanation, the narcotic taken with strychnine delayed the poison’s action for several hours, reconciling the timing with the final dose of medicine.

Misleading clues and family stakes

The murder was investigated amid repeated appearances of strychnine: it was present in Emily’s tonic, sold across the counter by Albert Mace at Styles St. Mary, and encountered again in the poisoning evidence handled within the household. Poirot regarded this abundance as confusing rather than conclusive. Each appearance needed to be assigned its proper place in the chain; the fact that strychnine was associated with several people and objects did not itself establish who had used it to kill Emily.

The family’s finances made the death immediately consequential. Emily’s will from the previous August left her entire fortune, after smaller legacies to servants, to her elder stepson, John Cavendish. Her earlier arrangement had been understood as a fair distribution because John was expected to maintain Styles, while Lawrence Cavendish would receive a considerable sum under their father’s will when Emily died. But Poirot established that English law automatically revoked Emily’s earlier will when she remarried. The legal position therefore made the existence, contents, and destruction of a later will particularly important to the investigation and to the household’s suspicions.

The will evidence also helped create a misleading prosecution case against John. The Crown presented Emily as a generous stepmother who had supported him and his wife in comfort at Styles Court, then argued that financial desperation, a quarrel, and an alleged intrigue with Mrs. Raikes supplied motive. It alleged that John had bought strychnine in disguise, intending to cast suspicion on Alfred. The defense countered that John knew his stepmother’s earlier will had been revoked by her remarriage, and argued that the evidence against Lawrence was at least as strong. These opposing accounts show how the murder’s legal and financial setting could make circumstantial evidence point in more than one direction.

Mary’s concealment and the final revelation

Mary’s actions after Emily became ill formed another apparent thread of the case. Believing that the sleeping draught she had given Emily was harmless, Mary nevertheless feared, when the word poison was heard, that Emily’s death might be her fault. In her panic she dropped Cynthia’s coffee cup and saucer into a large brass vase; Lawrence later found them there. She did not tamper with the remaining cocoa, which had been seen by too many people. Poirot’s distinction between testing for strychnine and testing for a narcotic explained why the cup’s concealment was incriminating in appearance but not evidence that Mary had poisoned Emily. Mary confirmed that Poirot’s account was true and described the episode as the most awful hour of her life.

The cup and cocoa were not the only objects whose meaning changed under closer examination. A stain on the carpet in Emily’s room was still damp, smelled of coffee, and held small fragments of china. Poirot inferred that Emily’s coffee cup had fallen from a tilting table and broken; the coffee was therefore not drunk. He further conjectured that she picked up the fragments, placed the cup on the bedside table, then heated and drank her cocoa. Since the cocoa contained no strychnine and the coffee had not been consumed, the medicine became the remaining route consistent with the evidence and the required evening timeframe.

Poirot said the attempt had been intended for Monday evening. Emily’s bell wire had been cut that day, and Cynthia was staying with friends, circumstances that would have left Emily alone in the right wing and cut off from help. But Emily forgot to take her medicine before going to a village entertainment, then lunched away from home the next day. The fatal dose was consequently taken twenty-four hours later than the murderer had anticipated. That delay allowed Poirot to obtain what he called the final proof, the last link in the chain, and to bring forward three thin strips of paper.

The explanation ended in public identification. When Alfred Inglethorp reacted to Poirot’s possession of the evidence and moved against him, Poirot evaded him and announced him as the murderer. The revelation closed the distance between the apparently scattered clues—the tonic, bromide powders, narcotic, broken cup, hidden cocoa, and altered timetable—and established their relation to a single concealed method. Emily’s death is therefore both the crime at the center of the narrative and the test of whether its evidence can be separated from the suspicions and false leads that surround it.