Lamont Granston [Rod La Rocque] assumes his secret identity as The Shadow to disrupt an attempted robbery at an attorney's office. When the police sweep the scene, Granston must impersonate the attorney, Chester Randall [John Elliott], to slip away unseen. Before he can depart, a phone call summons the attorney to the home of Caleb Delthern, a wealthy client who wants a new will drawn up. There, Delthern is shot, but not before he can state that his niece Marcia Delthern [Agnes Anderson] “is to be completely disinherited if she marries Warran” (Berringer).
The case grows tangled as inheritance motives come to light. The oldest nephew, Winstead Comstock [Walter McGrail], is arrested on suspicion since he stands to inherit half of Delthern’s vast estate, with the remainder to be divided among Marcia and two other nephews, Jasper Delthern [James Blakeley] and Humphrey Comstock [William Kellogg]. Winstead is later cleared of suspicion when alibis place him at a theater and a café at the time of the shooting.
Marcia discovers a pistol on Jasper’s night stand, and she and Humphrey contact Chester Randall [John Elliott] at his private line. Granston learns from Detective Kelly [James C. Morton] that the pistol found isn’t the same caliber as the weapon used in Delthern’s murder, and Marcia has Randall place the gun in the library desk drawer for safekeeping.
Chester Randall’s secretary Miss Hughes telephones Captain Breen [Kenneth Harlan], implying that Randall is in town when in fact he’s away on vacation. Breen tracks Granston to the Delthern residence and tries to verify Randall’s identity. Granston gets Breen to call his secretary back, while Granston’s assistant Hendricks [Norman Ainsley] discreetly disconnects the phone line—yet Granston answers as if the secretary is still connected. Breen is convinced and leaves, temporarily off the scent.
Meanwhile, Jasper owes casino club owner Barney Brossett [Cy Kendall] ten thousand dollars in gambling debts. Jasper tries to wring a larger eleven thousand loan from Winstead to pay him off, and a shooting erupts—Winstead is killed. Granston asks Breen to run a paraffin test on the pistol to determine if it was fired within the last two hours, then hands Marcia her uncle’s will to keep in a safe place.
Warran, suspicious of Granston’s true identity, notes that Randall’s phone line has been repaired and visits Randall’s secretary again. He learns that Randall was supposed to be away on vacation and informs Breen. Marcia goes to Granston’s home and warns him. Granston then pays a visit to Brossett as Hendricks sets up a listening device in Brossett’s window and overhears Brossett on the phone discussing how to obtain the will from the Delthern house and press Jasper to pay him to retrieve it.
Brossett’s men motor to the Delthern house to seize the will, but The Shadow appears and compels them to return the document. Delthern’s butler Wellington [Wilson Benge] finds Granston’s address in Marcia’s purse and goes to Granston’s place, declaring his intent to kill him. Brossett, now convinced that Granston is The Shadow, tails him to his residence and confronts him, while Wellington hides behind a curtain. The two men try to shoot Granston, but they end up killing each other instead. In his dying moments, Wellington admits that he had hoped to divert some of the Delthern money to his son, Warran Berringer [John Carnivale]. This revelation closes the circle on the motive behind the tension surrounding the inheritance and the danger surrounding the will.
