That Mainwaring Affair

In Short

Set among the turn-of-the-century Gilded Age elite, That Mainwaring Affair is a classic puzzle-box mystery centered on the suspicious death of stockbroker Hugh Mainwaring at his Fair Oaks estate. Following the discovery of the body, his written will disappears, unleashing a high-stakes struggle over his fortune between his prideful English relatives, a spurned former mistress with a illegitimate son, and a secretive young secretary who conceals his true lineage. Guided by shrewd attorneys and sharp private investigators, the plot unspools through courtroom battles, hidden motives, and shifted identities until a startling physical revelation unmasks the victim’s true identity.

The Story

The story opens in the luxurious New York offices of Mainwaring & Co. Stock Brokers, where senior partner Hugh Mainwaring hosts his aristocratic English relatives—Ralph Mainwaring and his son—and prepares to sign a new last will and testament. Hugh intends to leave his vast suburban estate, Fair Oaks, to his English nephew while largely disinheriting his secretive secretary, Harry Scott, and ignoring the claims of his housekeeper, Mrs. LaGrange, who insists her son Walter is Hugh's legitimate heir.

Tragedy strikes at Fair Oaks when Hugh Mainwaring is found shot to death in his private chambers. Simultaneously, the newly drafted will vanishes from the desk. Suspicion falls across the entire household. Mrs. LaGrange claims she confronted Hugh late at night over his betrayal, while servants report seeing a shifty stable boy named Brown discarding heavy objects into the estate lake. Detective Merrick and attorney Mr. Whitney investigate, but their efforts are complicated by the impassive demeanor of the secretary, Harry Scott, who bears the scrutiny with an unexpected, proud independence.

As legal battles erupt over the estate—pitting Ralph Mainwaring against Mrs. LaGrange's son—Scott quietly uncovers key clues. On a desk blotter, he discovers a peculiar signature left in dry ink: "Harold Scott Mainwaring." Recognizing the handwriting of his long-lost father, Hugh's disinherited twin brother, Scott realizes his father had returned from overseas and confronted Hugh in secret on the night of the shooting. To protect his father's honor and decipher the mystery, Scott travels to Australia and England under his true identity: Harold Mainwaring, the rightful heir to the original Mainwaring estate.

The mystery reaches its climax when private detective Dan McCabe tracks down a mysterious recluse living under an assumed name in a city tenement. Breaking into the room alongside Merrick, McCabe discovers the hidden man, who shoots himself before he can be taken into custody.

The final court hearing, Mainwaring vs. Mainwaring, turns on a shocking physical revelation. Examining the dead man's body, attorney Whitney and Ralph Mainwaring discover a distinct red birthmark above the right temple—a mark belonging exclusively to Hugh Mainwaring. The man murdered at Fair Oaks was not Hugh at all, but his long-lost twin brother, Harold, who had arrived that night to demand justice. Hugh had survived, fled the scene in panic, and lived in hiding under an alias until tracked down by McCabe. With the truth laid bare and the villainous Hugh dead by his own hand, the younger Harold claims his legitimate inheritance, leaves cursed Fair Oaks behind, and embarks on a new life in England with his beloved Winifred.

How It Unfolds

The gathering at Fair Oaks Hugh Mainwaring hosts his English family to settle his estate, drawing up a fresh will while his bitter housekeeper, Mrs. LaGrange, overhears his plans and vows revenge for her disinherited son.

Murder and a missing will Hugh is found shot dead in his tower apartment, and the newly drafted will disappears, prompting a formal coroner's inquest that casts suspicion on the impassive secretary, Harry Scott.

The stable boy's testimony Witnesses reveal that a disgruntled stable hand named Brown was seen acting suspiciously and throwing a heavy, unknown object into the estate's lake on the night of the crime.

Secrets on the blotter While copying documents in the tower room, Scott notices a unique signature pressed onto a desktop blotter, giving him his first real clue that another Mainwaring visited the house before the shooting.

The battle in court Competing legal claims divide the estate between Ralph Mainwaring's faction and Mrs. LaGrange, while Scott adopts his true identity, Harold Mainwaring, to uncover his father's past.

Cornered in the alley Detective McCabe tracks the elusive key figure to a tenement at No. 545 Jefferson Street, breaking down the door only to hear a fatal gun report from within.

A twin's birthmark revealed At the final hearing, witnesses identify a faint red birthmark on the deceased man's temple, proving that the victim at Fair Oaks was the twin brother, while the real Hugh had fled to the city.

The People

• Hugh Mainwaring: A wealthy, cold, and calculating New York stockbroker who seeks to disinherit his past obligations. He desires complete control over his estate, but his scheming unravels when his past catches up to him, driving him into hiding and ultimately to a desperate end.
• Harry Scott / Harold Mainwaring: The refined, methodical private secretary to Hugh. He wants to clear his name, honor his father's memory, and claim his rightful legacy. By keeping his composure through intense suspicion, he exposes the truth and wins both his inheritance and the heart of Winifred Carleton.
• Mrs. LaGrange: The vengeful housekeeper at Fair Oaks who claims to be Hugh's secret wife. She wants recognition and wealth for her son, Walter, but her manipulative schemes fall apart under cross-examination when her long history of duplicity is exposed.
• Ralph Mainwaring: Hugh's arrogant English relative who demands the fortune for his own family branch. Driven by greed and pride, he fights fiercely against all rival claims until confronted by the horrifying revelation of the family secret.
• Dan McCabe: An unpretentious, sharp-eyed private investigator who disguises his brilliance under an unassuming exterior. He wants to solve the mystery through quiet observation, ultimately delivering the case's biggest breakthroughs.

In Its Own Voice

"You defrauded your only brother during his lifetime; you have persistently ignored your son, your own flesh and blood; and now you would rob him, not only of his father's name, but of his father's fortune..."

Mrs. LaGrange fiercely confronts Hugh Mainwaring in the library late at night, overheard by the secretary.

"I've no time to waste with you, Mr. Merrick; we may have a desperate piece of work on hand; but if you'll come with me, I give you my word for it that before this job is over you'll meet the biggest surprise of your life."

Private investigator Dan McCabe warns Detective Merrick right before they force open the door to the suspect's hideout.

"It was the mark by which, when we were boys, he was distinguished from his twin brother."

Ralph Mainwaring stammers in shock upon identifying the birthmark on the casket at the final hearing.

What It's Really About

Beneath its procedural surface of missing wills and courtroom drama, That Mainwaring Affair examines the destructive power of greed and false identity within aristocratic family lines. The novel contrasts the artificial respectability of Gilded Age social status with moral integrity. Hugh Mainwaring's life of deception—denying his twin brother, his mistress, and his offspring—shows how corporate wealth and grand country estates often mask bitter personal corruption. The central conflict relies on physical and moral mirroring: twin brothers whose outer resemblance hides vast differences in character. Ultimately, the story argues that truth cannot be buried under legal maneuverings or hidden identities; secret sins inevitably break through polished surfaces to demand justice.

Why Read It Today

Fans of late-Victorian detective fiction and Gilded Age melodrama will find That Mainwaring Affair a captivating historical gem. It blends the methodical clue-gathering of classic turn-of-the-century mysteries with the high-stakes courtroom tension of a sensation novel. The prose is dignified and paced with methodical precision, offering rich atmospheric descriptions of opulent Manhattan offices, grand suburban mansions, and shadowy city alleyways.

Modern readers should be prepared for period-typical features, including slow-burning legal procedural scenes, formal dialogue, and dramatic character archetypes. Additionally, brief appearances by minor working-class characters feature heavy nineteenth-century dialect spellings. Yet the novel holds up remarkably well thanks to its tight plotting and clever use of forensic identity twists. Anna Maynard Barbour constructs a genuine narrative puzzle where every detail—from desk blotters to hidden birthmarks—matters. It leaves the reader with a satisfyingly complete resolution where justice prevails over greed.