In Los Angeles, Lorraine W. Brinckley runs the Brinckley Art Gallery with Norton Benedict as a silent partner. Benedict has recently acquired a very rare Gabriel Mantegna painting and is going to Italy to buy a companion piece. Meanwhile, in Milan, famed detective Michael Waring, known as "The Falcon" and working as an investigator for the International Surety Company, buys the second painting, on approval, from artist Giuseppe Donatti and his associate, Martin. Later, Donatti admits that the painting is a fake, executed by him, and that he has sold a similar painting to the Brinckley Art Gallery. That night, Michael is awakened by Benedict, who is attempting to steal the painting. Benedict escapes without the painting and leaves a gun behind. The next morning, Michael discovers that Donatti has been murdered. When he returns to Los Angeles, Michael shows insurance company chief Fred Muller the painting. Muller reveals that in 1945, when it was discovered that during the war the two paintings had been stolen from the estate of Count Dalo, his company had paid the count $80,000. Now, if Muller can recover both paintings, the count will have to repay the insurance settlement. After Michael tells Muller that the painting is a fake, he takes it to the art gallery, looks at the one on display there and tells Lorraine that they are both fakes, although she insists that they are genuine. Michael proposes that they form a partnership to sell both paintings. She agrees, and they deposit them in the left luggage area of Union Station. Michael then tears the claim checks in half, gives one half to Lorraine and tells her that when she finds a customer, they will reclaim the paintings together. After driving Lorraine home, Michael spies on her as she hides the claim tickets on the back of a painting. Later, Benedict returns from Italy and Lorraine tells him about her new partner. One night, Michael enters the closed gallery and finds an account book in Lorraine's desk that details substantial payments to Benedict. While Michael is reading the book, he is interrupted by Martin, who is also breaking in. Michael beats him in a fight, then turns him over to the police. Later, when Lorraine tells Michael that she has a customer interested in buying the paintings, he switches her claim checks so that when she goes with Benedict to the station and attempts to outwit Michael by claiming that her niece tore up the checks and presents the false ones, the clerk brings her a bird cage and a small box. Meanwhile, two thugs take Michael to a warehouse and beat him up in order to get him to tell them where the paintings are, but Michael outsmarts them in a gunfight and escapes. Later, Michael invites Benedict to see the paintings at the gallery but when he produces them, Benedict draws a gun on him and is joined by Lorraine. Michael cleverly is able to make a wire recording of the ensuing conversation in which Benedict admits killing Donatti as he was about to flood the market with fakes. Lorraine is surprised to learn that the paintings really are fakes, then when she unwraps them, she finds only blank canvasses. Michael then suggests a three-way partnership and tells them that the paintings are in his hotel's vault. The next morning, when the hotel clerk hands Michael, who is accompanied by Benedict and Lorraine, a receipt to sign, Michael secretly writes a message telling the clerk to call the police. The clerk does this, takes the paintings from the vault and returns to the front desk with a gun. Benedict shoots the clerk, after which Michael jumps on Benedict, but Benedict gains the upper hand and, using Lorraine as a shield, tries to escape. Just then the police arrive and overpower him, but during the confusion Lorraine escapes. Michael and the police soon find her at the gallery, where Michael says that Benedict has exonerated her and that the two paintings, unknown to Benedict, are actually genuine. Finally, Lorraine agrees to sell the paintings for the count so that he can repay the insurance company. Michael declares the case closed and leaves with Lorraine to discuss a more romantic partnership.