The episode kicks off with the caretaker, Chris Brooker, Kelvin Fitzwalter, portrayed by Rob Ostlere, and a police officer forcibly entering Harry Franklin's apartment, only to discover his lifeless body. Meanwhile, Patience Evans, played by Ella Maisy Purvis, gently places her bearded dragon back into its enclosure just as Douglas Gilmour, admirably essayed by Adrian Rawlins, arrives with a package in hand. As Patience unwraps the box, Gilmour solemnly breaks the news of Franklin's demise.
At the police station, DCI Calvin Baxter, masterfully enacted by Mark Benton, summons DI Bea Metcalf, brought to life by Laura Fraser, to collaborate on the Franklin case. Later, at the crime scene, Patience meticulously examines Franklin's body until Elliot Scott, portrayed by Tom Lewis, steps in to capture some photographs. Franklin's novel, "Overture," triggers a nostalgic flashback to young Patience, played by Ava Cook, engrossed in an Agatha Christie mystery, gifted to her by George Evans, portrayed by Jamie Maclachlan.
Switching back to the present, Metcalf hands Patience a pair of gloves for protection. Dr. Loretta Parsons, played with finesse by Liza Sadovy, reveals that potassium cyanide was the cause of death. Patience postulates that it could have been hydrogen cyanide instead, to which Parsons responds that potassium cyanide is more prevalent. Patience persists, arguing otherwise in this particular scenario, prompting Metcalf to caution her against publicly contradicting the doctor.
Kelvin, representing Pardona Publishing, claims to have been worried when Franklin failed to respond to his messages for three days. Notably, Pardona Publishing isn't Franklin's publisher, but Kelvin had approached him with a proposal to pen a memoir. The caretaker clarifies that Franklin never left the premises and didn't own any electronic devices, last speaking to him three days prior about posting a letter. Parsons later informs Patience that hydrogen cyanide was detected on a glass, prompting her to note its almond scent, reminiscent of Franklin's beloved Amaretto Liqueur. She notices he was drafting a letter to Lottie when Elliot reprimands her for touching the Olivetti typewriter, causing her to storm out.
Upon returning home, Gilmour notices Patience's distress. She confesses to tampering with evidence at the crime scene, fearing that Metcalf will revoke her role as her assistant. He reassures her that everyone makes mistakes. Outside the York City Police Department, Patience anxiously awaits Metcalf, who arrives late. She apologizes and hands her a file on Franklin. Baxter informs them that the public believes Franklin's death to be a homicide. Patience concurs, stating he was murdered, yet no hydrogen cyanide was found in the Amaretto. Metcalf emphasizes the urgency to uncover how the poison ended up in Franklin's glass. DS Jae Hunter, played by Nathan Welsh, reveals that Franklin recently opened his first domestic bank account in two decades, with a six-figure deposit from Pardona Publishing. She notes the absence of any memoir drafts in his apartment and the missing letter to Lottie. DC Will Akbari, portrayed by Ali Ariaie, mentions that Franklin's former publisher was Halfpenny Publishing, owned by Pippa Junor, played by Shereen Martin, adding another layer to the intricate tapestry of this mystery.
Kelvin steadfastly denies having received any memoirs from Franklin, while emphatically asserting his own honesty. Metcalf chimes in, stating categorically that his flat contained no such documents. He further alleges that Franklin had assented to penning an account of the blaze that had narrowly spared his life. Intriguingly, she presents Kelvin with a photograph depicting Harry alongside a woman and another man, whom he promptly identifies as Edmund Lennox, an author in his own right (played by Christopher Osikanlu Colquhoun).
Elsewhere, Patience draws inspiration from a refreshing glass of iced lemonade, sparking a revelation. She hastens to the police station to enlighten Metcalf about the seven varieties of locked-room mysteries, particularly highlighting the ingenious "ice arrow" technique, wherein the murder weapon mysteriously vanishes. She elucidates that hydrogen cyanide, subtly infused into water, was frozen into ice cubes. Metcalf, acting swiftly, despatches Hunter to request Parsons to scrutinize the ice trays for traces of the poison.
Shortly thereafter, Metcalf confronts Pippa about CCTV footage capturing her presence at Franklin's flat on the preceding Saturday. Pippa brazenly recounts her encounter with Franklin, painting him in a condescending light. Later, Metcalf confirms to Patience the accuracy of her theory concerning the poisoned ice cubes. Patience, in return, shows her a newspaper clipping detailing the cabin fire that claimed Lisa Newman's life and nearly fatalities Lennox and Franklin. The cabin was owned by Aldous Tate (portrayed by Rupert Holliday Evans). Franklin had requested copies of the incident report and Newman's autopsy just two weeks prior.
Patience notices that Lennox possesses an Olivetti typewriter identical to Franklin's. Lennox reveals that Aldous had attempted to seduce Newman and confirms that Newman had a twin. Metcalf then fills Lennox in on Franklin's memoirs. Subsequently, Will informs Metcalf of a second, unsupervised entrance to Franklin's apartment, which CCTV overlooked. The footage also catches Aldous lurking outside Franklin's apartment complex on the fateful Saturday. Hunter reveals that Aldous was dismissed from his position after multiple students accused him of sexual harassment. Franklin had reached out to Aldous four times in the past fortnight.
When confronted, Aldous refuses to utter a word without legal counsel. Patience informs Metcalf that "Adam's Island," attributed to Lennox, was actually Franklin's creation. Lennox disputes this claim vigorously. Patience assures him that the Jaccard Index will unmistakably prove Franklin's authorship. Lennox explains it was an arrangement between them; when the novel was shortlisted, they decided to keep their collaboration under wraps until after the award announcement, believing it best to let the secret rest with Franklin. As they depart, they learn that cyanide residues have been discovered on Aldous' clothing. At the precinct, Hunter formally charges Aldous with Franklin's murder.
Patience pondered why Franklin, whose hand had been cruelly scarred in the fiery accident, would opt to use a manual typewriter. Soon after, Marissa Wilson (portrayed by Alix Wilton Regan) burst into Baxter's office, dumping an assortment of files onto his desk with a dramatic flair. She revealed that hydrogen cyanide, a naturally occurring substance, was present in the plants cultivated in Penny Tate’s (played by San Van Roy) greenhouse. With a stern warning, she threatened legal action against the department for wrongfully imprisoning Aldous, unless he was promptly released. Moments later, Aldous walked out of custody a free man.
Metcalf and Patience ventured to visit Pippa to examine Franklin’s inaugural Fortnum manuscript. Patience keenly observed that the indentations left by Franklin’s left-hand keys were notably weaker compared to those made by his right hand. She adamantly maintained that Franklin could not have authored the Fortnum novels, as the manuscript exhibited no such disparity. Declaring that she was ill-suited to be Metcalf’s assistant, Patience departed abruptly.
Later, Patience attended a meeting of an autistic support group, while elsewhere, Metcalf arrived at the grim scene of Aldous’ demise. In the trunk of his car, Franklin’s memoirs were discovered, and the cause of his death was confirmed as hydrogen cyanide poisoning. Parsons reported that Newman had been stabbed. Baxter pondered aloud the inexplicable reasoning behind Aldous’ apparent suicide.
Patience scanned the memoirs and deduced that they were penned by the same individual who had written the letter to Lottie. Metcalf revealed that Franklin had reached out to Lottie, seeking information about her sister, Lisa Newman. Upon scrutinizing a typewritten document, Patience noted that it, along with the Fortnum manuscript, had been typed on distinct machines. Metcalf clarified that it was a page from Franklin’s notes, actually authored by Lennox.
Lennox confessed to penning the Fortnum novels solely for financial gain. Hunter presented him with a 2004 Tortuga National Bank statement jointly held under his and Franklin’s names. Metcalf accused him of opening the account and lavishly compensating Franklin. Lennox claimed that Franklin had suffered immensely due to the fire, but Metcalf countered by accusing him of murdering Franklin to prevent him from exposing Lennox as Newman’s stabber. It transpired that Lottie had been terrified of Lennox, rather than Aldous, whom Lennox had framed to take the blame. Lennox admitted to killing Newman out of a desire to be with Franklin. Metcalf then showed him Franklin’s letter, which falsely implicated Aldous in Newman’s murder.
Later, to Metcalf’s astonishment, she learned that Patience had refrained from opening a puzzle box that once belonged to her mother, Mathilde Hendricks.
