A radio sleuth infiltrates the Brooklyn Dodgers to solve a murder.

After New York police inspector Holcomb discovers the slain body of Sergeant Malcolm in a Sheepshead Bay lighthouse, he concludes that the policeman was killed by the mysterious "Constant Reader," whose typed note led authorities to the spot. As with three previous murders about which Constant Reader has written, the note describes the crime scene in exact detail. Soon after, government reformer Grover Kendall criticizes Holcomb for his failure to solve the string of murders and gives him another Constant Reader note. This one directs the police to the body of a long-missing gangster. While dredging up the body from the Hudson River, Holcomb hears a broadcast of The Fox radio show, in which the crime-solving "Fox," played by Wally Benton, discusses a fictitious "murder" letter. Because Wally's fictitious letter bears a striking resemblance to the latest Constant Reader note, Holcomb declares Wally the killer. Before the police find him, however, Wally and his bride-to-be and co-star, Carol Lambert, are accosted in Wally's dressing room by cub reporter Jean Pringle. Jean, who was alerted to the performers' impending elopement by Chester, Wally's dim-witted assistant, begs to accompany them on their honeymoon, but Wally and Carol refuse. Chester, an aspiring publicist, then casually tells Jean that Wally is Constant Reader, making Jean all the more determined to follow the couple. Just as Wally is about to leave with Carol and Chester, the police show up to arrest him. Thinking that they have been sent by his co-workers as a prenuptial gag, Wally teases the police and is startled when they begin shooting at him. Confused, Wally flees in his car with Carol and Chester, an ex-convict who confesses that, as a publicity stunt, he wrote the last Constant Reader note on Wally's typewriter with information he had acquired from his old gangster friends. After Wally, Carol and Chester finally stop at a Brooklyn warehouse, Wally sends Chester to arrange a peaceful surrender with the police. Unknown to Chester, his call is overheard by someone at the station, who alerts gangster Creeper and his thugs to Wally's whereabouts. Wally and Carol, meanwhile, discover Jean hiding in their car trunk, and to Carol's annoyance, the reporter begins to flirt with Wally. Just then, Creeper and his gang arrive and open fire on Wally and his companions, who assume the attackers are policemen. The foursome seeks cover on top of a freight elevator, which then breaks and almost kills them. When the police finally arrive at the warehouse, they engage in a gunfight with the gangsters, whom they assume are Wally and his cohorts. After the police chase off the gangsters, Wally decides to disguise himself and sneak into the police station to discover what is happening. Chester joins Wally and, upon studying photographs of Constant Reader's victims, Chester realizes that they were all involved in the conviction of a notorious gang leader. Wally then concludes that Constant Reader's next victim will be Kendall, who spearheaded the investigation, and determines to save him. Unknown to Wally, Kendall is actually the secret head of Creeper's gang and is also Constant Reader. As soon as Wally and his friends burst into his house to warn him, Kendall imprisons them at gunpoint. Kendall, who intends to become the undisputed king of crime, then announces that he is going to stab Holcomb while he is seated next to him at a Brooklyn Dodgers game and frame Wally for his death. Although Creeper is assigned to guard the foursome, Wally manages to escape and rushes to the Dodgers' stadium, Ebbets Field. Unable to get close to the heavily guarded Holcomb and Kendall, Wally knocks out a pitcher for the opposing team, the bearded Beavers, and dons his uniform and long beard. While posing as the pitcher, Wally throws a baseball with a warning message on it to Holcomb, but Holcomb fails to see it. After Wally inadvertently tosses the ball into Kendall's hands, Kendall alerts the police that Wally is in the ballpark. Kendall then sets his murder plan into action, but is thwarted by Wally. Despite his heroics, Wally is unable to convince Holcomb of Kendall's guilt and is pursued through the ballpark by both the police and the gangsters. Escaping in a taxicab, Wally rushes to free his friends, unaware that Kendall has already instructed Creeper to dispose of them. At Kendall's, Wally finds a recording made unwittingly by Carol, in which Creeper reveals where he is taking his prisoners. After Wally sends the taxicab driver with the recording to Holcomb, he races to the docks, arriving just as Creeper and two other thugs are about to throw the chained-up Carol, Chester and Jean off a boat. Wally tricks the crooks into believing he is the police, then grabs one their guns and starts shooting off the chains. When his gun runs out of bullets, Creeper and the other thugs descend on him, and a long chase ensues. At the police station, meanwhile, the taxicab driver finally convinces Holcomb to listen to Carol's record, and the police head for the boat. By the time they arrive, however, Wally has already apprehended all of the criminals, including Kendall. At last cleared of suspicion, Wally enjoys a much-needed kiss from Carol and looks forward to his honeymoon.