Ivy (portrayed by Cathy Belton) tenderly attends to William 'The Duke' Wellington (Stuart Martin) as he convalesces. Her nurturing presence is disrupted by the entrance of Eliza Scarlet (Kate Phillips), who discovers her belongings strewn across the table. Inquiring about William's condition, Eliza gently urges him to continue his rest, her concern palpable as her fingers briefly graze his hand before sheplayfully remarks that she cannot indulge in such leisure.
Transitioning to the office, Eliza is met with an unexpected revelation from Clarence (Paul Bazely): Patrick Nash (Felix Scott) has returned. In a confidential exchange, Nash laments the precarious state of his business, while Eliza defends herself, arguing that his employees' reluctance to work under a woman is hardly her fault. She asserts that positive changes are afoot. Nash, however, stands firm in his decision to remain in London until his venture regains its footing.
Post the introduction, Clarence reassures Eliza that he did not solicit Nash's return, although he did keep him apprised of their progress. Nash heads to The Fat Goose, a haunt frequented by the Metropolitan Police, journalists, and legal eagles of the Royal Courts of Justice. Meanwhile, Eliza prepares for a crucial meeting with a wealthy and influential client. Nash insists on accompanying her to their conversation with Jack Carter (Oliver Bennett) and his spouse, Maisie Carter (Emma Edmondson).
The conversation veers into the aristocracy's disdain for nouveau riche. Jack brushes it off, emphasizing that he cares little for their opinions as long as Maisie is treated with respect. He derides them as pretentious snobs. Stafford offers tea, recounting how they hosted a charity event for The Ladies of the Mayfair Benevolent Society, of which Maisie is a member. Tragedy struck two hours in when Admiral Nelson's diamond feather, an auctioned treasure cherished by Jack, was stolen. Nash suggests compiling a guest list and the names of the staff working that night. Jack is convinced a guest is the culprit and vows to double their fee upon the thief's apprehension.
Returning to the office, Eliza suggests Nash offer an apology, but he stubbornly refuses. She learns that Nash has been receiving letters from his former employees. Clarence steers them back on course, focusing their energies on the case. Nash tasks him with delivering the completed contract, insisting he is there purely to assist. Eliza delves deeper into the guests' backgrounds, joined by William, who inquires about her day, having heard of Nash's return from Oliver Fitzroy (Evan McCabe).
William is in no hurry to return to his workplace, as the entire establishment seems to be crumbling around him, prompting him to even contemplate never stepping foot back into it. The recent incident has opened his eyes to a multitude of considerations, foremost among them being his future. His mind drifts back to their initial encounter in the kitchen, interrupted by Ivy's grievances about her mother.
Later that morning, Eliza informs Nash that she might have uncovered something intriguing concerning one of their guests. He inquires about the background checks she conducted on Jack Carter. Nash elucidates that Jack had acquired his textile factories with the earnings from his original venture, revealing that he hails from a notorious criminal clan in Northern England. Nash berates her for her lack of thoroughness and promptly sends a telegram to Jack, declining to take on his case.
Jack Carter bursts in, vowing to handle the situation with composure and civility, as he had promised Maisie. He insists that they undertake his case and recover his stolen jewel. Should they fail, he holds them personally accountable. As a gesture of compensation for insulting his character, he offers their services free of charge. Once Jack exits, Nash emphasizes the urgency of locating the thief. Eliza mentions that Admiral Nelson's relatives had reluctantly put the feather up for auction the previous year. Scanning the guest list, she notices the name Lord Fallon. Lord and Lady Fallon support a charity dedicated to aiding retired Royal Navy sailors, establishing a kinship with Admiral Horatio Nelson; Lord Fallon is Nelson's cousin.
Disguised as patrons of the arts, Eliza and Patrick pay them a visit. Patrick reveals that the Carters are business acquaintances of the Fallons. Lady Emily Fallon scorns Jack for making a fool of himself and hints that her husband is no better. Eliza observes a red mark on Emily's neck. Later, Eliza and Nash quiz the Fallons about the feather, which is virtually a family heirloom. Mr. Fallon suspects Baroness Weichmann, citing her overwhelming debts as motive. Outside, Eliza reprimands Mr. Fallon for the bruises marring Emily's neck.
Meanwhile, Ivy and Oliver Fitzroy observe William. Oliver confesses that today is crucial as he is set to visit the American Embassy, his heart set on securing the secondment above all else. Enchanted by the prospect of being in New York, Oliver craves William's attention for his speech. Eliza and Nash then proceed to visit Baroness Weichmann, who is in the midst of selling her estate. Eliza mentions Maisie Carter, but before they can elicit any responses, a guest arrives for the baroness.
In a confidential moment, Eliza confides in Nash, revealing that the gentleman in question is none other than Mr. Gibson (Paul Murray), an underhand dealer specializing in illicit art and jewelry. Back at the office, they task Clarence with uncovering more about this enigmatic figure. An anonymous letter soon arrives, asserting that the diamond feather rests within Lord Fallon's ornate writing desk.
Later, Oliver pays William a visit, venting his frustration over being passed over for the promotion. He muses that a new position in New York could have marked a clean slate, far from the shadows of his and his father's past. Apparently, they were seeking someone with a more extensive resume, akin to William's. Before departing, William offers Oliver a word of encouragement, acknowledging his prowess as a detective. Meanwhile, Ivy imparts some wisdom to William, suggesting he would make a wonderful father and urging him not to squander his life's limited moments. Nash devises a plan to bribe one of Lord Fallon's maids, gaining them clandestine access to the mansion. Eliza, skeptical of the ease of their endeavor, inquires about the contents of Nash's men's letters, but he tight remains-lipped. Nash concedes that the situation was not her fault, blaming himself for entrusting her with the responsibility.
After the Fallons depart, they slip into the mansion like shadows, making a beeline for Lord Fallon's desk. Eliza confesses to having dismissed one of Nash's men, though he assurances them they would have deserted anyway. Their hearts race as they hear footsteps approaching, forcing them into concealment. Peering through a crack, they witness another figure rifling through the desk before making a swift exit. Eliza and Nash leave, contemplating that the diamond feather might now be in other hands.
The next morning, William seeks out Eliza, intent on a private conversation. When she mentions her client, worry etches across his face, fearing for her safety. Eliza hastily exits, dodging a deeper discussion. Meanwhile, Clarence presents a compilation of dealers in stolen luxury goods but draws a blank on Gibson. Undeterred, Eliza believes she knows just where to track him down, and sets off to do so with renewed determination.
Gibson steadfastly denied any acquaintance with Baroness Weichmann until Scarlet revealed she had witnessed them together. She alleged that Weichmann was pressuring Gibson to peddle a pilfered artifact. In his defense, Gibson insisted that every item in his possession was authentic and above reproach. Scarlet persisted, claiming that The Duke had whispered tales of Gibson's involvement in illicit goods. Conceding defeat in that argument, Gibson admitted to compensating Weichmann solely for bringing him affluent clients, unbeknownst to their spouses, who entrusted him with valuables to sell. He also mentioned a pending appointment with Emily later that day.
Upon returning to the office, Nash and Scarlet found Maisie and Jack eagerly awaiting an update on their case. Nash promised to keep them informed of any developments. After Stafford escorted Maisie to her carriage, Jack confided that his family was mocking him about the theft, giving Nash and Scarlet a 24-hour ultimatum to provide him with names and addresses.
The Duke found himself grappling with the task of articulating his affections for Scarlet in a letter. After much deliberation, he finally confessed his love for her. Meanwhile, Gibson shared with Nash and Scarlet that Emily intended to sell Admiral Nelson’s diamond feather to finance her divorce. Scarlet pondered aloud if Lord Fallon had originally stolen it from Jack, only for Emily to now lay claim to it. Clarence added fuel to the fire by revealing that Emily had booked the Marlborough Suite at the Brabham Hotel, paid for by Jack, hinting at a clandestine affair between the two.
Just as The Duke was about to present Scarlet with his heartfelt letter, Clarence barged in with an urgent message from Gibson, scheduling a meeting for 4 PM. Scarlet reassured The Duke that she would be ready for dinner by 8 PM before rushing out. He left his letter on her desk, but a flashback of Arabella Acaster's warning echoed in his mind—that Scarlet's ambitions would ultimately overshadow her feelings for him. Haunted by this thought, he retrieved the letter.
Upon entering her suite, Emily is confronted by Scarlet and Nash, who await with accusations about the diamond feather. She steadfastly denies any wrongdoing until Nash produces the incriminating evidence, just as Maisie bursts in, adding an unexpected twist to the confrontation.
Later, amidst the tension, Emily reveals that their paths had crossed through the Mayfair Ladies’ Society, where they commiserated over their unhappy marriages. Maisie interjects, claiming that Lord Fallon physically abuses Emily whenever he's intoxicated. Emily then admits to stealing the diamond feather as retribution against Jack for coercing her into relocating to London. Maisie confesses that she had inadvertently placed the jewel in Lord Fallon’s desk, hoping Jack would eliminate Fallon, thereby sparing Emily the ordeal of a divorce. Overwhelmed by the guilt of potentially causing Fallon's demise, Emily reclaimed the feather. Maisie, worried about Jack's retribution, expresses her fears for their safety.
Scarlet and Nash later deliberate on the best course of action against Jack. They return the diamond feather to him but remain tight-lipped about the case’s intricacies. Jack, insistent on answers, finds himself confronted by Scarlet's threat to expose his connections to multiple disappearances. She asserts that had the police known, he would already be incarcerated. Scarlet hints at possessing incriminating intelligence gathered from his party guests, warning that his aspirations to infiltrate London's elite circles, akin to Admiral Nelson, would be dashed if his true colors were revealed. She strikes a deal, promising to keep his secrets in exchange for double their usual fee, which Jack reluctantly accepts.
Celebrating their victory, Nash, Scarlet, and Clarence toast to their success. Nash praises Scarlet, lamenting that his men failed to recognize her as both a remarkable woman and an exceptional detective, suggesting they start anew. As they clink glasses, Scarlet realizes the late hour and hastily departs for home, eager to find The Duke's letter. Upon her arrival, he enters the room, announcing his decision to take a temporary post in New York. Confessing his love for her, he declares that he cannot bear to be near her without being with her. They share a passionate kiss before he exits, leaving her to watch his carriage disappear into the night. The episode concludes on this poignant note.
