As the curtains draw shut on the thrilling finale of "Miss Scarlet & The Duke," Eliza Scarlet (portrayed by Kate Phillips) and Patrick Nash (Felix Scott) find themselves in a harrowing dash for freedom, dodging bullets like pros. Patrick, breathless and anxious, mentions a bygone era when a certain type of chemical was produced there, yet the specific details elude him. Desperate for refuge, they stumble upon a hiding spot and struggle to secure the door, their every move urgent and fraught. Eliza, having administered a sedative to their pursuer—a formidable figure indeed—hopes the potion will soon take effect. Patrick's memory flickers back, recalling that the place once thrived as a dye works for clothing. The giant threatens to burst through just as his strength wanes, collapsing moments before breaching their sanctuary. Nearby, vials of dye topple over, their vivid hues spilling in chaotic patterns.
Back at the station, Eliza and Patrick receive accolades for capturing the fugitive, Eliza cautioning her colleagues that their workload is poised to soar even higher. In a confidential exchange, Clarence (Paul Bazely) commends them, asserting that this quarter marks their strongest performance yet. Patrick, however, reveals plans to return to Paris by week's end, expressing concern for Eliza's evident fatigue, the result of relentless, seven-day workweeks stretching back months. He suggests an escape to the horse races, philosophizing about the futility of amassing wealth if one cannot indulge in the occasional frivolity.
Elsewhere, DS Charlie Phelps (Tim Chipping) and Oliver Fitzroy (Evan McCabe) lament the challenges posed by The Duke's absence, Oliver confessing ignorance of his father's intentions regarding the skipper's position, suspecting the Hudson rumors to be mere hearsay. Enter Commissioner Fitzroy, who seeks a private audience with his son. He reveals the pressing need for a competent replacement for Wellington during his New York stint, dismissing Phelps due to the job's newly acquired political tinge. Hudson and five others have already declined, the Commissioner acknowledging how expansion has turned the role into a perilous proposition—hence his contemplation of Oliver. To test Oliver's mettle, he assigns him to lead the next murder investigation.
Eliza excels at the races, her spirits high as she returns to the precinct with Patrick. Clarence beams with news of the Harrison case contracts finally materializing. Patrick, meanwhile, receives a telegram that leaves him visibly startled. At dinner with Ivy (Cathy Belton) and Mr. Potts (Simon Ludders), Barnabus leads them in grace, while Eliza shares news of a letter from William received earlier that morning. Potts, unable to contain his excitement, teases a tale about methanol received at the mortuary, adding an eerie undertone to the evening's conversation.
Oliver approaches Eliza with a matter of grave delicacy, seeking her company as he searches frantically for Nash, whose whereabouts remain elusive. A grim incident has occurred: a murder in Aldgate, where the victim was repeatedly stabbed on a bustling street. Nash is now a person of interest in this grim saga, with Oliver carrying an arrest warrant in his possession.
At the crime scene, Oliver unfolds the perplexing details. The deceased's identity remains shrouded in mystery, save for the fact that he frequented a local tavern, where he was known only by his first name, Eamonn. Phelps reveals that Nash had also been in that same tavern, inquiring about Eamonn with an air of urgency. The landlord, who recognized Nash's agitated demeanor, later witnessed him standing over the lifeless body before fleeing the scene.
A disagreement sparks between Phelps and Oliver over Oliver's authoritative role in the investigation. Eliza, expressing her ignorance of the man in question, stands firmly by her conviction that Patrick Nash is not capable of such a heinous act. Phelps presses further, inquiring about Nash's location.
At the precinct, Clarence informs Eliza that Nash's whereabouts are unknown, and he admits to being unaware of the contents of a recent telegram. Clarence further clarifies that he is responsible for compensating their informants, with one exception: Eamonn Murray. He once engaged a cab driver to divulge Nash's whereabouts, possibly leading to his address. Driven by curiosity, Eliza visits Murray's apartment, where she discovers a tin can lying inconspicuously on the floor.
Meanwhile, Oliver seeks an update from Mr. Potts, who reveals that the coroner's report is still pending. Phelps notes that Eamonn Murray has never been entangled with the law. Oliver, frustrated, demands to know when the postmortem examination will be conducted.
Returning to the office, Clarence confesses his intentions to betray Nash's trust, driven by his genuine concern for him. Nash, it transpires, makes a monthly payment to a woman named Margaret Farrel. Eliza secures Margaret's address and proceeds to visit her, only to find her absent. Speaking with Margaret's husband, who is equally searching for her, Eliza learns that a noisy neighbor had mentioned a mysterious visitor named Patrick, who comes and goes when the husband is away. Mr. Farrel's revelation deepens the mystery: he pulls out a tin can identical to the one Eliza found earlier, hinting at a possible connection. He warns Eliza sternly against involving him in her search further.
Eliza then visits Mr. Potts once again, but to her disappointment, learns that Oliver Fitzroy is absent, and Mr. Wormsley has yet to complete the postmortem report.
Eliza attempts to leverage her connection with Ivy to gain access to the morgue, but Potts steadfastly refuses her entry. Undeterred, she trails him, imploring him with every step. She reveals that she seeks his expert insight, a tactic that appears to sway him. Eliza expresses her curiosity specifically about the deceased man's teeth. Soon after, she encounters Oliver, who informs her that Eamonn has dispatched a telegram to Nash, announcing his return. Eliza remains puzzled by this revelation and suggests they discuss it at dawn. Oliver, however, is too consumed by the urgency to solve the case and secure his promotion to rest easily.
Upon entering, Eliza informs Nash of his message's receipt. Nash, desperate, implores her to abandon her pursuit, warning that the individual she encountered is perilous. When Eliza mentions the chewing tobacco and comments on Eamonn's pristine dental condition, Nash's plea intensifies, urging her to stay out of it before hurriedly departing.
The following day, Eliza presents the tobacco tin to Oliver and Phelps, believing it to be the key to unmasking the murderer. She elucidates that Eamonn and Margaret were Nash's informants. A man fitting the Irishman's description was observed at Eamonn's residence on the fateful day. This particular tobacco is exclusive to a single shop in London, nestled near the docks, which recently sold several tins to the crew of a Norwegian fishing boat named the Narvik. Among them was an Irishman who purchased three tins. Eliza has already procured the ship's manifest, revealing Sean O'Driscoll as the sole Irish name listed. They resolve to track him down by the docks.
In a private moment, Oliver confesses to Eliza that balancing rebuke with encouragement, as William once did, does not come instinctively to him. Eliza reassures him, conviction in her voice, that he will carve his own path. At the docks, Oliver informs the locals of their quarry. Initially uncooperative, Charlie leverages his father's legacy in the merchant navy, warning them of potential questioning and subsequent job loss. One man eventually steps forward, identifying another who had sailed on the Narvik. Their suspect flees, but Oliver swiftly tackles him, only to receive a headbutt in return. Phelps steps in, and Oliver strikes from behind. They escort him to the station to interrogate him about Sean O'Driscoll. The man claims they assumed Sean would return home, where he supposedly resides, but instead, he stayed with them.
This sequence of events paints a vivid picture of Eliza's relentless pursuit of truth, intertwined with the dynamics of camaraderie and conflict among the investigators.
On the second evening, he stumbled back late, intoxicated, furious, and drenched in blood. Sean threatened him with death unless he claimed to have been present throughout the night. This confrontation occurred two nights prior to the murder. When questioned about Sean's whereabouts, specifically if he was still at the boarding house, tensions were high. As the team prepared to storm the boarding house, Oliver revealed to Eliza some crucial documents he had unearthed from the Clerkenwell records office. Eliza verified that they indeed belonged to the same individual, who happened to have an arrest warrant dating back to 1876. He was once a suspect in the murder of Michael Nash, Eliza's revealed, Patrick's brother.
Returning to the office, Eliza inquired about Michael Nash with Clarence. Clarence disclosed that someone had accessed the concealed safe in her office, leading him to believe Patrick had returned. The safe contained items Patrick might need to vanish without a trace. Clarence scrutinized the office to ascertain if anything else had been taken.
While awaiting the raid on the boarding house, Oliver attempted to mend fences with Charlie, suggesting it would be beneficial for them to be on better terms. Charlie was unmoved, urging Oliver to either do his job or refrain from patronizing him. Meanwhile, Eliza observed orange dye on the safe, speculating that Nash might have returned to the factory. Rushing there, she confronted Nash, who inquired about her findings. Eliza revealed her knowledge of Sean's guilt in Michael's murder and Patrick's pursuit of him.
Nash disclosed that Sean was nearby, tied up. Patrick admitted having two witnesses to his brother's murder, Margaret and Eamonn, whom he had kept on his payroll over the years. They had agreed to alert him if Sean ever resurfaced. When Eamonn did just that, Patrick reached him too late, prompting him to relocate Margaret to a safe place. Patrick confessed his intention to execute Sean. Eliza begged him not to, saying she had been told all her life that there were things she couldn't do, and Patrick was the only one who had ever believed in her. She emphasized that he was her business partner and friend.
Just then, Sean began to free himself, grabbing a shard of glass, forcing Patrick to shoot him. Later, Oliver informed Eliza that Sean, though seriously injured, would survive. Phelps argued that self-defense could be a plausible defense. Eliza admitted Patrick had saved her life but acknowledged that they couldn't overlook the charges of obstruction and kidnapping. If convicted, Patrick faced a stint behind bars.
Eliza is granted permission to converse with him within the confines of his cell. Patrick reveals that his license will be revoked pending his trial, implying that the officer will have to close the case temporarily. Confident in his network of reputable lawyers and High Court judges, Patrick harbors hope that this will merely be a fleeting obstacle. He suspects, however, that Eliza finds it hard to believe him. She insists, with determination, that she will manage just fine. Patrick yearns for her to perceive him in a favorable light, to which Eliza playfully retorts that such a transformation is highly unlikely. Undeterred, Patrick vows to continue his endeavors.
At the Fat Goose Pub, Commissioner Fitzroy expresses his dissatisfaction with the establishment and proceeds to announce that the job is Oliver's for the taking. Oliver declines, emphasizing his contentment with his current role and the abundance he still has to learn. When his father expresses disappointment, Oliver confesses that such sentiments no longer trouble him. He suggests another candidate who would be most suited for the position. Phelps steps into the breach while William is absent, gratitude shining in his eyes as he thanks Fitzroy.
Back at home, Eliza's thoughts drift back to her conversation with William, reflecting on how drastically things have unfolded. Mr. Potts, Ivy, and Clarence lend a helping hand as she prepares to relocate. Eliza promises Clarence that she will reach out once she is back on solid ground. Meanwhile, Mr. Hill completes his task, painting Eliza's name with pride atop the sign of the private detective agency, now hanging proudly above the door.
