Synopsis
When Blevins Playfair receives compromising photographs of himself in the mail, accompanied by a blackmail request for "Twenty Grand," spelled out in newspaper clippings, he is desperate, knowing that the only way to pay would be to have his wealthy brother Justin, who has assumed the dress and demeanor of the famous fictional detective Sherlock Holmes, committed to an asylum, allowing Blevins to seize control of the family fortune. Although Blevins' amiable wife Daisy admires Justin's keen abilities of observation and deductive reasoning, Blevins finds him annoying, especially when Justin grabs the blackmail note and vocalizes his musings on its hidden clues. That morning, Blevins goes to a clinic endowed by the Playfair family to speak with administrator Dr. Strauss, who assures him his chief psychiatrist, Dr. Mildred Watson, will sign Justin's commitment papers. Mildred refuses because she is consulting with a patient, Mr. Small, who refuses to speak, and has not had time to examine Justin, but when Justin, in full Sherlock Holmes attire, arrives at the clinic with Daisy, Mildred is fascinated by his display of "classic paranoid" symptoms. Using deductive reasoning, Justin determines that Small does not speak because he is silent film star Rudolph Valentino. Small smiles and immediately begins to talk with Justin, leading Mildred to announce that she must examine Justin more closely. Later, as Justin is analyzing the blackmail note in the nineteenth century-style laboratory he and Daisy have set up, Mildred arrives to speak with him. Justin hides in a secret passage as Blevins and Daisy explain that Justin had been a brilliant judge and reformer but has acted as Holmes since his wife Lucy died a year before. When a bemused Mildred says that Justin must be hiding from his archenemy, Professor Moriarty, Justin exits his hiding place, after which he verbally spars with her, saying that he has read everything Justin Playfair wrote and knows that he was driven mad because he tried to make the world a better place. He then says that the blackmail note's "Twenty Grand" is the "master clue" to Moriarty's "master plan" and begins to tell her things he has deduced about her, but when he realizes that her name is "Dr. Watson," he urges her to come with him to 20 Grand Street, which he thinks explains the clue. Although reluctant, Mildred is swept up by his enthusiasm and takes a taxi with him to the address, which turns out to be the telephone company. After insisting she take a gun, they enter the building and witness a young woman named Grace pleading with an information operator for the address of her new boyfriend, who called to tell her that he had taken an overdose of sleeping pills. The operator refuses to give her the information, then, with tears in her eyes, quits her job and tells Grace the address. Meanwhile, at the clinic, after Blevins pressures Strauss to have the commitment papers signed that afternoon, he is picked up by Mr. Brown, a thug who warns him to get the money or Justin will be killed. Later, Justin takes Mildred to one of his favorite haunts, a movie theater that plays old Westerns, which appeal to Justin because of their purity. Beloved by the assorted characters who inhabit the balcony, Justin tells Mildred that he has enjoyed working with her, and she admits that his observations about her lonely, work-filled life were correct. When one of the homeless men in the balcony awakens and starts a disturbance, Justin drags Mildred out of the theater and continues through Times Square, pondering clues. Seeing a bag that reads "Back to School," he thinks it is another clue, then becomes embroiled in an argument when a man refuses to put a bag of litter in the bin. After Mildred fires her gun in the air to stop the argument, they take a taxi to see Justin's old friend Wilbur Peabody, who works in the library basement and has known him since he was a boy. Cranky because she has lost one of her shoes and fired a gun, Mildred says she cannot help Justin and angrily leaves. Returning to her apartment, she gets an angry phone call from Strauss, who orders her to bring "that paranoid" back to the clinic, but she hangs up on him. The next morning, when Wilbur returns to the library, Holmes is still there and encourages him by saying that Mildred will return. Just then, she, too, comes back and shows him a headline about his apparent disappearance and tells him that Blevins only wants his money. She then chats with Wilbur about the clues they have found and Justin suddenly announces that someone named bag must run a school. After saying that he likes her very much, he takes her to the Bagg School of Horticulture, which he found in the telephone book. On the top floor of a deserted building, they find a riding academy owned by the elderly Baggs, who have not left the premises since 1939 and turned it into a magnificent garden filled with the topiaries that they lovingly created. After the Baggs serve tea and ask Justin to criticize their work, they are shocked by the arrival of Brown, who says that he is a friend of Blevins. Seeing that Brown is hiding a pistol, Justin and Mildred escape with the help of the Baggs. That evening, Mildred, dressed in a frilly prom dress, ineptly prepares dinner for her pre-arranged evening with Justin. When he arrives through the fire escape, they shyly talk, and Justin suggests that, after the case, they go to some of the fashionable places in New York, telling her not to worry over his attire as he has many more suitable "costumes" to wear. As they start to dance, a shot rings out and Justin collapses. Mildred begins to cry and call him "Holmes," pleasing Justin, who soon comes to from his slight wound. Feeling that the attempted murder shows Moriarty's desperation, he takes Mildred with him for a midnight rendezvous with his archenemy. Walking through the cold, dark streets of Manhattan, they first encounter Wilbur, who is wearing a plumed hat like his literary hero, The Scarlet Pimpernel. They soon are joined by Daisy, who is leaving Blevins because she no longer loves him, and eventually are joined by Mr. and Mrs. Bagg, Mr. Small and a sympathetic nurse who has helped him to escape, Grace, her boyfriend and the information operator. With Justin's band of happy followers behind them, they march along until Justin stops on a deserted street. The others are confused that no one is there, but Justin tries to spur them on to follow him to his rendezvous in the tunnels below. As Justin and Mildred walk down the stairs beneath the street, Mildred turns around and notes, sadly, that no one is following them, but Justin says that he cannot blame them. The pair soon come to an opening to the street and see a supermarket. Justin tells Mildred that he loves her, and she says that she loves him, too. He then leads Mildred inside the sterile, virtually empty supermarket in which the manager droningly announces specials over the public address system. Moments later, Justin's invigorated followers enter the store and swarm through the aisles, causing chaos as they pull things from shelves and loudly express their frustrations against entering police. To avoid the increasing pandemonium, Justin and Mildred step into the market's meat locker, where Justin re-analyzes the clues, certain that he has misinterpreted something. When Mildred says that "Twenty Grand" was also the name of a racehorse, Justin is sure that she is right and deduces that the rendezvous point must be near the riding school near Central Park. As midnight approaches, Mildred accompanies Justin to the park, where they walk toward a tunnel. When Justin says that he hears the horses' hooves, Mildred at first hears nothing, then joyfully tells him that she can hear them. As the sound of the trotting horses becomes louder, Justin asks her to stand close, saying that they must find them very close together. They then look toward the bright light emanating from the tunnel as the sound of the horses' hooves increases.
