Humphrey Campbell, a seasoned private detective, tracks down a runaway woman named Louise Campbell and ends up marrying her. On the way to Reno, Nevada, for their honeymoon, the newlyweds stop at a bank that is robbed by three men, a twist that foreshadows the dangers ahead.
Oscar Flack of the Flack Missing Persons Bureau tracks the couple to a Reno hotel. Louise persuades him to take a case after he promises her a fur coat for locating Hal Benedict, the missing man. They travel to meet Warren Benedict, Hal’s father. When Humphrey learns the FBI may be involved, he resists, but Oscar convinces him to proceed. Despite his attempts to shield her, Louise remains determined and tags along, drawn into a case that quickly grows more tangled than expected.
In the hotel bar, Humphrey learns that Hal was seen frequently with a woman; Irene Donovan is the person in question. A blonde named Gypsy Toland offers him a ride to Irene’s place, but a furious Louise exposes their presence and he exits the car. Later, Humphrey discovers Irene is dead, while Rose Madden — Hal’s fiancée — is found alive and protesting that she did not kill Irene. The pair end up driving Rose’s car, parking, and talking, and Louise notices Humphrey in the company of Rose. With Louise now suspected of complicity and her husband under a murder cloud, the tension intensifies.
Humphrey seeks out Clyde Copley, a collections investigator who admits he was hired by Hal to retrieve letters Hal wrote to Irene; Irene had threatened to use those letters if Hal married Rose Madden. Eventually, Humphrey is exonerated when Police Chief Police Chief Bates learns that his alibi is solid.
Warren Benedict wants to see Humphrey, but a deadly confrontation ensues as three men shoot at them while heading to Benedict’s ranch. In the ensuing shootout, Humphrey wounds two assailants and drives them away. He also identifies a silver dollar found in Irene’s hand as the hallmark of Red Harris, a notorious bank robber. Benedict then reveals a ransom note demanding $50,000 for Hal’s return and instructs Benedict’s foreman Harry Belding to deliver the money that night. Humphrey urges obedience to the plan.
Two FBI agents confront Humphrey, convinced he is the bank robber they’re after, but Oscar vouches for him. Later, Harry Belding is murdered and robbed while on the way to deliver the ransom.
The plot thickens when Gypsy Toland lures Humphrey into an abduction; Red Harris intends revenge on Stafford, Humphrey’s crooked lookalike. Red must be convinced that Humphrey isn’t the man he seeks, and Humphrey deduces that Red doesn’t know any suspects by their real names. He proposes an audacious setup: Red should stand outside a window to identify the person who truly knows him by that famous trademark. Louise, caught snooping near the scene, offers to be Red’s hostage to seal the plan.
As tensions converge, Humphrey gathers everyone in Clyde Copley’s office, and Red fails to spot any familiar face. A tense shootout with FBI agents—prompted by an anonymous tip—leads to Red Harris’s death, and the remaining truth surfaces. In the end, Humphrey concludes that the killer must be Clyde Copley himself, bringing the case to a dramatic and fitting close.
