Spots 
Kingdon Cole keeps watch on Professor Carmody's apartment through a foggy October night in New York. A mysterious luxury limousine pulls up along Bleecker Street, interrupting his vigil. Inside, an enigmatic woman calling herself Miss Brown knows Cole's name and intimate details about his investigation. She convinces him to step into her car, offering cryptic warnings about his futile watching.
CHAPTER I
Miss Brown leads Cole into a windowless, richly paneled luxury suite hidden behind an ordinary elevator shaft. Despite the plush armchair and elegant surroundings, Cole quickly realizes he is a prisoner in this concealed sanctuary. Miss Brown returns transformed into a glamorous figure in rose silk, pleading with him to drop the Carmody case. She insists the forces behind the mystery are too vast and perilous for one detective to fight.
CHAPTER II
Left in total darkness, Cole searches the silent room until a speaking tube embedded in the wall crackles to life. Miss Brown's frantic voice warns him through the hidden mouthpiece that ruthless men intend a fate far worse than death if he refuses their terms. Hearing an intruder creep across the carpet in the dark, Cole readies himself for an ambush. Lacking matches or light switches, he relies entirely on his sharpened physical senses to meet the oncoming threat.
CHAPTER III
Bound on a cot, Cole confronts the tragic reality of Malcolm Reeves, the missing man he was hired to locate. The once brilliant scholar has been reduced to a babbling, vacant shadow of his former self, repeatedly muttering about colors. Mentioning Professor Carmody momentarily triggers a flash of terror and dormant memory in Reeves' shattered mind. Cole realizes that Carmody and his conspirators engineered Reeves' mental destruction to neutralize him without causing a physical death.
CHAPTER IV
A sinister black-bearded surgeon prepares an ether sponge to perform a mind-destroying operation on Cole, placing surgical blades nearby to break his spirit. Turning this cruelty into an opportunity, Cole secretly grasps a knife between his bound hands while pretending to be dazed. As the surgeon leans down to deliver the anesthetic, Cole loops his manacled arms around the man's neck and secures the blade with his teeth. He fights back using sheer leverage and desperate tactical instinct.
CHAPTER V
Escaping his captors, Cole returns to his apartment to tend to his cat Toots before consulting Doctor Dickson Latham about his physical exhaustion. Latham appears suave and evasive, offering polished medical advice while subtly challenging Cole to uncover his true nature. Analyzing the doctor's evasions, Cole connects Latham's physical appearance to the black-bearded surgeon who tortured Reeves. He leaves convinced that Latham is an artful rogue using medical expertise as a front for conspiracy.
CHAPTER VI → CHAPTER VII
Miss Brown telephones late at night, summoning Cole to another clandestine meeting in Madison Square while warning that he is under heavy surveillance. Cole effortlessly shakes off a clumsy shadow outside Gramercy Park before slipping into the waiting limousine. Miss Brown reveals that her organization has maintained constant, expert espionage over him that far exceeds standard street tailing. She blindfolds him once more, leading him back toward the hidden headquarters of her shadowy cabal.
CHAPTER VIII
Cole stands before the council known as The Unknown Seven, led by the stern criminal lawyer Grover Carlin. Their initial friendliness turns to sharp suspicion when a red warning light flashes inside a glass indicator globe, signaling an intruder operating the secret elevator. Carlin accuses Cole of compromising their hidden lair, as he is the only recent outsider allowed inside. Cole defends his integrity, pointing out that an insider or former executive must have betrayed their security controls.
CHAPTER IX
A piercing scream cuts through the council chamber, ending abruptly as Malcolm Reeves is murdered in a back corridor. Cole rushes toward the escape route, catching a fleeting glimpse of a hunchbacked assassin fleeing into the private elevator. Refusing to let the killer escape, Cole leaps open-handed into the shaft, gripping the descending steel cables with bare hands. He slides down twenty floors at breakneck speed, defying death to intercept the killer at the building's lower levels.
CHAPTER X
Tracking the hunchbacked killer to Doctor Latham's brownstone, Cole poses as a patient seeking relief from a headache. During their tense conversation, Cole notices a fresh dark bloodstain on the physician's pajama cuff beneath his dressing gown. Latham maintains a cool Machiavellian demeanor, refusing to confirm or deny the hunchback's presence in his basement. Cole recognizes that the doctor and Professor Carmody are actively coordinating to eliminate witnesses and cover their tracks.
CHAPTER XI
Cole pushes past Latham into a back room, finding the hunchback unconscious from a heavy hypodermic dose administered by the doctor. Latham claims the man is a sick patient who cannot be moved, cleverly thwarting Cole's attempt to make an immediate arrest. Outmaneuvered, Cole steps to the office desk and dials an independent physician for an immediate consultation. Terrified of an outside doctor exposing the fabricated medical condition, Latham is forced to reconsider his unyielding stance.
CHAPTER XII
Receiving a supportive note signed with seven X's, Cole sets out to relocate the mysterious organization's headquarters without a recorded address. Assisted by clues from an associate, he identifies the Security Building, an unpretentious office tower with standard commercial listings. Analyzing the ground floor lobby, Cole spots a doorway marked Private tucked between the elevator shaft and the service stairs. Instinct tells him this hidden portal conceals the private elevator leading straight to the secret council chamber.
CHAPTER XIII → CHAPTER XIV
Returning to Carlin's office, Cole discovers a hidden microphone disk mounted inside a central ventilation shaft with wires running to the roof. Realizing an insider has bugged the council, Cole instructs Carlin and Miss Brown to maintain mundane conversation while he devises a trap. He suggests hosting an all-inclusive dinner where everyone must drink a sauterne toast as a pledge of loyalty. Cole plans to manipulate the traitor's fear of poison to force a public self-betrayal.
CHAPTER XV
During the banquet, Cole pretends his sauterne toast trick was a complete failure, allowing the traitor to feel entirely secure. Doctor Ballinger, a cheerful council member, consolingly mocks the failed psychological trap, assuming his composure hid his guilt. In reality, Cole's sharp gaze caught Ballinger's momentary flash of panic before the doctor regained control. Keeping his discovery secret, Cole directs young operative McKendrick to trace the dictaphone wire across the building roof to locate the master receiver.
CHAPTER XVI
Cole enters a side room and discovers McKendrick shot dead, placed on the exact cot where Reeves previously lay. Investigating the missing body of Reeves, Cole deduces that the killers removed it via the roof to prevent an autopsy. A medical examination would have revealed a specialized surgical procedure on Reeves, pointing direct suspicion at professional surgeons like Ballinger or Latham. The conspirators left McKendrick's body as a threat while carefully hiding the surgically altered remains of their primary victim.
CHAPTER XVII
Cornered on the roof by Professor Carmody at gunpoint, Cole refuses to hand over coded letters recovered from the scene. Knowing Carmody lacks personal honor and will shoot if he turns, Cole uses psychological misdirection by staring intently at a point above Carmody's head. Unnerved by Cole's fixed, unblinking gaze, the professor grows anxious and glances backward to see what is behind him. Cole seizes that momentary split-second distraction to disarm Carmody and escape down the fire ladder.
CHAPTER XVIII
Cole sneaks into Doctor Latham's residence at night, hiding as the physician investigates strange scratching noises in the hall. Latham finds the hunchback using matches to pick the lock of an old storage room safe, searching for confidential papers. After Latham leaves, Cole observes the hunchback's subtle satisfaction, realizing the fellow successfully retrieved or inspected secret documents. The encounter confirms that rival factions within the conspiracy are actively spying on and betraying one another for personal gain.
CHAPTER XIX
Learning that Miss Brownell has been kidnapped, Cole joins forces with Doctor Latham, whose genuine devotion to her safety transcends his villainy. Tracking the conspirators north, they navigate a boat through rough waters into a wild section of Dutchess County. High atop Dutchess Point, an abandoned cliffside resort accessible by an old cable car line, they spot lights from an anchored yacht and motorcars. Cole and Latham scale the dark, rugged peak together to infiltrate the enemy's heavily guarded mountain fortress.
CHAPTER XX → CHAPTER XXI
Infiltrating the tower, Cole finds Miss Brownell guarded by armed men outside her room. He whispers to her to conduct a staged argument, using his ventriloquism skills to make his voice sound like it originates from across the chamber. They discuss fabricated suspicions about Latham, convincing the guards outside that Cole is unprepared and isolated. When two guards enter to exploit the situation, Cole ambushes them in quick succession, knocking both unconscious and freeing Miss Brownell without firing a shot.
CHAPTER XXII
Overpowered by reinforcements, Cole wakes up with a swollen jaw alongside Doctor Latham and Miss Brownell in a shuttered room. Professor Carmody arrives to threaten them, demanding the key to an alchemical process known as the seventh ingredient. Latham realizes the gang vastly exaggerates the importance of this minor chemical component, believing it essential for synthetic gold production. Cole advises Latham to play along with the delusion, using their supposed possession of the formula as a bargaining chip to protect Miss Brownell.
CHAPTER XXIII
Carmody returns with news that the chief has rejected Latham's terms, but Latham counters by inventing a fiction about dangerous electronic reactions. The doctor glibly claims that attempting the process without his guidance will cause a catastrophic explosion. Carmody's pseudoscientific ignorance makes him swallow the lie completely, leaving him shaken and hesitant to act. Cole marvels at how the gang's obsessive desire for synthetic gold makes them easily manipulated by confident scientific double-talk.
CHAPTER XXIV
Taken to the executive office, Cole faces the true leader of the alchemists: Englebreth, a wealthy invalid in a wheel chair who poses as a civic benefactor. Englebreth reveals he used his access as a vice president of the Bureau of Civic Research to spy on The Unknown Seven. He admits that Cole's arrival was the first real threat to his scheme of producing vast quantities of gold in subterranean vaults. Expecting to murder his prisoners, Englebreth freely boasts of his grand criminal enterprise.
CHAPTER XXV
Bound and left without weapons, Cole secretly hands Doctor Latham a long, sharp tie pin hidden under his coat lapel. When Englebreth returns with armed guards to force the formula from them, Latham leaps forward, holding the sharp pin against Englebreth's neck. Latham threatens to pierce the invalid's jugular instantly if the guards make a move. Terrified for his life, the invalid chief retreats with his guards, granting the prisoners a crucial reprieve while they seek a permanent escape route.
CHAPTER XXVI
Tapping the room's walls while Latham kept the guards distracted, Cole located a hollow section that conceals an old gambling resort escape panel. Creeping through the secret passage into the night air, Cole overpowers a sentry, ties him up, and takes his automatic pistol. Armed once more, Cole prepares to launch a decisive surprise attack against Englebreth's forces to rescue his companions and destroy the gold syndicate. The secret passageway transforms a hopeless captivity into the key to complete triumph.
CHAPTER XXVII → CHAPTER XXVIII
A detective unravels a high-stakes conspiracy of secret societies, medical deceit, and synthetic gold.