Jim goes to the Star Warehouse in St. Louis at the request of scarred gangster Johnny Sabatini. The wheelchair-bound mob boss wants a private talk with Jim and orders his men away. Sabatini then tells Jim that he needs his help because he's dying. He offers him another mobster, Harry Boorman. But first Sabatini explains that he wants Jim to protect a woman. Jim is to find a man named Swanson in Calliope, MO, and give him a key. When Jim wonders why Sabatini chose him, Sabatini explains that the agent is the only one he can trust, even among his own organization. Boorman will try to stop Jim so Jim can capture him. The woman knows Sabatini as "Mr. Caroline" and Sabatini doesn't want Jim to tell her differently. Before he can explain more, Sabatini has a seizure and mutters "the Madonna statue" with his dying breath. Jim takes the key, the card with the woman's address, and Sabatini's cigar, and leaves.
At the Wanderer
, Jim meets with Colonel Richmond and chemist Ned Brown. Ned confirms that the cigar was poisoned with curare. They figure that someone killed the dying Sabatini to keep him from having Jim go to Calliope. Ned and Richmond are aware that a $500,000 Army payroll was stolen in Calliope and never recovered. Captain Nolan, who engineered the operation, was murdered by his own gang when he tried to cheat them. Richmond okays Jim to go to Calliope and meet Swanson, but also assigns Ned to meet with the woman in St. Louis. All they know about Boorman is that he has a leg injury and Richmond isn't convinced that Sabatini was telling the truth. However, Jim believes the mobster was telling the truth and heads for Calliope.
Ned and Agent Bowlers go to the address and Ned meets with a young woman, Sylvia Nolan. Sylvia is glad to see someone from Mr. Caroline and Ned realizes that she's blind. The girl asks what happened to Sabatini, who provided for her, and Ned breaks the news to her. He tells her that Sabatini left a gift for her.
Jim rides into the near-deserted town of Calliope. Sheriff Chayne is seated outside his office and admits that there aren't many people left in town. Jim asks about Swanson and Chayne directs the agent to the edge of town. Fabian Swanson is the town mortician and is resting in one of his coffins. Swanson assumes that Jim wants a coffin and shows off his best product until Jim displays the key. Before Swanson can respond, Chayne comes in and subtly threatens Swanson, claiming that he came to check on Jim. Swanson writes a note to Jim, claiming it has prices, but it warns Jim not to say anything and to come back later. Jim plays along as Chayne warns him that all the talk of Nolan's treasure is just gossip. The sheriff then invites Swanson and Jim to dinner but Jim declines and heads for the hotel.
After Ned leaves, Bowler hears something outside of Sylvia's house, goes to investigate, and gets knocked out. Meanwhile, Sabatini's servant Clarence visits Sylvia, claiming he wanted to check on her. He asks about the gift Sabatini left her but she doesn't remember anything about her early life before Sabatini made her his ward at the age of seven. Clarence mentions Calliope and Sylvia finds the name familiar but can't place where she heard it. She asks Clarence to take her to Calliope, insisting that it's important and could bring things back to her. Clarence agrees to take her along.
That night in Calliope, Jim has dinner at the hotel dining room. Chayne, Swanson, and several townspeople are there, and the sheriff talks about the treasure-hunters who have come to Calliope in the past. The shopkeeper, Farnsworth, remembers some of them but points out to Jim that Calliope offers more than rumors of treasure. The storekeeper is positive that Calliope will turn itself around once the railroad comes through, and tells the hotel owner, Snidley, that he will soon have hundreds of guests. An older woman, Melanie Nolan, comes in to complain to Chayne about the streets and is surprised to discover they have guests. She sits down for supper and talks about how Calliope was once a magnificent town. Chayne points out that her brother was the one who stole the payroll, and Jim challenges him on it. Swanson hastily interrupts to leave for the mortuary and Chayne asks if he's working on his land office business. Jim gets up to bed down his horse and Melanie asks him to check her harness traces.
Outside at Melanie's carriage, Jim checks the traces and assures Melanie that they're fine. She invites him to visit him at her home, Sans Souci, and then bids him a good night. Jim then goes to Swanson's mortuary and finds Swanson's glasses on the floor. Swanson is in a coffin, dead, and Jim hears someone moving in the back. When he checks the back alley, three thugs jump him. One runs off and Jim gives chase, and runs into Ned. The man escapes and the other two men have disappeared from the alley. Jim tells Ned about Swanson's death and Ned explains about Sylvia. They figure that a church would be the logical place to look for a Madonna statue but the local church burned down. Ned heads to the cemetery to look for the Madonna while Jim prepares to ride out to talk to Melanie. Chayne comes by and Ned claims to be a passing stranger. Once Ned leaves, Jim tells the sheriff that Swanson is dead and leaves as well.
Jim rides to Sans Souci but gets no answer at the door. He goes inside and looks upstairs, unaware that Clarence has brought Sylvia there. She has scattered memories of the house and Clarence encourages her to try and remember. Jim finds them as Sylvia says that she's sure that she's been in the room before. When Jim interrupts them, he asks why Clarence is there and the servant says that he's helping Sylvia find the present Sabatini left her. When Jim prepares to take her back to St. Louis, Clarence flies into a fury, charges at Jim, and falls over the balcony to his death. Someone begins playing the harpsichord in a neighboring room and when Jim and Sylvia follow the noise, they find Melanie at the keyboard. She welcomes Jim but is surprised to see Sylvia, who she recognizes. Melanie faints and Jim goes to her, but notes a cameo of a younger Melanie... and Sylvia.
At the cemetery, Ned looks for a Madonna statue and spots the Nolan mausoleum. The door is locked but he uses Sabatini's key to open it and go inside. There are crypts for Valerie and Edmund Nolan but no sign of a Madonna statue. He finds the crypt for Captain Aylmer Nolan, who has a scar on his face just like Sabatini's, and Ned realizes they are one and the same. Two thugs enter the mausoleum and Ned uses a windup noisemaker to distract them long enough so that he can slip out.
At Sans Souci, Jim revives Melanie and she explains that she was shocked to see her brother Alymer's daughter Sylvia. Sylvia doesn't remember her but Melanie describes their childhood adventures. She explains that Sylvia's mother was killed in the church fire, and Sylvia remembers a brutal man who was there, demanding to know where stolen money was from. The man burned down the church and the trauma affected her memory, but all Sylvia can remember is that the man dragged his foot because of a leg injury. There's a knock at the door and Jim goes to answer it. Once he leaves, Melanie rips off her gray wig, revealing herself as a much younger woman.
Jim finds Ned at the door and the chemist explains that Sabatini was Nolan. Meanwhile, Sylvia remembers that Boorman was the man who came after her and her mother the night of the church fire. While the girl talks about the night of the fire, Melanie goes to the patio and confirms that Boorman is outside, lurking in the shadows. Sylvia talks about how her mother was frightened of Boorman and his demands for the money. They hid in the room and somehow escaped to the church. Boorman enters the room and Sylvia hears his limping step, while Melanie encourages Sylvia to remember where the money was hidden. She fumbles at the mantelpiece and finds the hidden catch that opens a secret panel. Boorman limps toward her and Sylvia hears him and scream.
Jim and Ned hear Sylvia's scream and run upstairs. Sylvia has made her way to the yard and is fumbling her way through the bushes, with Melanie in pursuit. The girl hides, realizing that Melanie isn't who she claims, and the imposter continues on. However, Sylvia can still hear Boorman coming after her.
Jim runs through the forest and finds Sylvia at the cemetery. He takes her into the Nolan mausoleum and asks if she remembers if there has ever been a statue there. Sylvia remembers a Madonna statue and a tall man who showed it to her. The pedestal where it rested is empty, and when Sylvia twists it, Alymer's crypt slides out of the wall. The limping Farnsworth and the fake Melanie come in, Farnsworth holding a shotgun, Sylvia recognizes Farnsworth's voice as Boorman and he introduces "Melanie" as Laura Semples, his greedy accomplice. Sylvia grabs a vase and knocks it over, distracting Boorman so that Jim can disarm him. However, Snidley, Chayne, and the two thugs arrive and explain that everyone in town was in on the treasure hunt except for Swanson.
The townspeople open Alymer's crypt but there's nothing inside but dust. Ned comes in with a derringer and Jim jumps the thugs. After a brief fight, the two agents dispose of the men and examine the coffin. Buried in the dust is an envelope addressed to Sylvia. It's from Sabatini, stating that the attached document leaves Sylvia her inheritance: all of the Nolan properties in and around Calliope.
Later back at the Wanderer
, Ned boasts that he saved Jim, covered himself with glory, and rescued Sylvia. He's decided to take a well-deserved vacation on a desert island and departs, whistling.