A gambling-ship owner is out to fleece a beautiful society woman, but falls in love.

As the lone figure of a woman paces the New York docks one foggy night, Hard Swede, a sailor, tells the night watchman about her. Swede, the former captain of the gambling ship Fortuna , explains that the woman is waiting for the return of the ship and its owner, gambler Joe "the Greek" Adams, but adds that the ship will never return because it is sitting on the bottom of the Atlantic Ocean. Swede then relates the following story: Just prior to America's entry into World War II, the Fortuna is about to sail for Havana when Joe and his partner, Zepp, receive their draft notices. Protesting that he fought his war by crawling out of the gutter, Joe decides to circumvent the draft by assuming the identity of petty criminal Joe Bascopolous, a dying sailor who has been classified 4-F. Joe and Zepp, who has also been classified 1-A, roll the dice for the ownership of the boat and Bascopolous' 4-F card, and after Joe wins the roll, Zepp goes to the draft board and is himself classified as physically unfit to serve because of a heart condition. Joe is searching for a way to raise money to sail when socialite Dorothy Bryant approaches him on the street and asks him to buy a ticket to the War Relief charity ball. Realizing that the ball offers a perfect way for him to raise the money, Joe visits the all female War Relief office and suggests that a gambling concession at the ball could easily raise $100,000 to send medical supplies to Europe. Captain Steadman, the head of the organization, is charmed by Joe and his idea, but Dorothy protests that gambling is illegal. After leaving the draft board, Zepp, meanwhile, returns to the ship and finds a letter from the parole board addressed to Bascopolous, notifying him that he is in violation of his parole and will be automatically imprisoned for life if he commits one more criminal offense. Zepp pockets the letter and, after lying that he has several weeks to report for duty, asks to stay onboard the boat. Joe, undaunted by Dorothy's opposition, returns to the War Relief office to enlist as a recruit and Dorothy puts him to work knitting. The next day, Joe wins Dorothy's admiration when he uses a trick coin to get McDougal, a purveyor of used blankets, into donating his merchandise to the war effort. When Dorothy asks Joe why he is so interested in aiding her organization, he sees some newspaper headlines announcing the Nazi invasion of the Varda Valley and tells her that his family lives there and he just wants to do his part. Feeling guilty, Dorothy invites Joe to accompany her to the docks, where Comstock, a supplier, has refused to unload a shipment of supplies without payment. At the docks, Joe follows Comstock into his office and strongarms him into releasing the supplies. In the struggle, Comstock tears Joe's jacket and Dorothy insists on bringing him home to repair it. On the drive home, Joe teaches Dorothy a form of rhyming slang in which the words "my darling" would be transposed as "briny marlin." Joe thinks that Dorothy invited him home for romantic reasons, and when she denies this, he offers to settle their differences by playing the same coin game he used on McDougal. When Dorothy incorrectly assumes that he plans to trick her, Joe, insulted, coldly informs her that his motto is "never give a sucker an even break, but don't cheat a friend." Joe's words shame Dorothy into offering him the gambling concession, and a triumphant Joe returns to the ship and informs his gang that they will soon sail to Havana with the ball proceeds. Joe requires $6,000 to start the games rolling, and consequently, when Dorothy writes a personal check in the same amount as a deposit on a freighter, Joe offers to deliver the check to Hargraves, the shipping commissioner. At the commissioner's office, Joe watches as Hargraves endorses the check and then convinces him that it is unpatriotic to demand a down payment. Chagrined, Hargraves returns the check and Joe pretends to tear it up. When Joe cashes the check, Dorothy's grandfather, Mr. Bryant, notifies the police, who then visit the War Relief office to arrest Joe Bascopolous for parole violations. After the police appear at the office, Dorothy pretends that Joe is the water man and arranges to meet him later that afternoon. Picking him up in her car, Dorothy, who hates Joe's loud ties, presents him with a new tie and drives him to her country house in Maryland. When they arrive, she tells him about the police and calls her grandfather and threatens to marry Joe unless he calls off the police. Resenting Dorothy's threat, Joe accuses her of feeling superior to him, but she denies this and kisses him. They then drive back to New York, and after dropping Dorothy at her house, Joe speeds away, confused. Later, Joe appears at Dorothy's door, and after asking her to reknot his tie, he kisses her. That evening, before the ball, Joe asks Swede about Bascopolous, and Swede shows him a letter, written in Greek, addressed to the dead sailor. Taking the letter to a Greek priest for translation, Joe learns that the letter is from Bascopolous' mother, notifying him that his two brothers have died while defending their village from the Nazis. After the priest comforts him with a prayer, Joe goes to the ball, puts $6,000 in an envelope addressed to Hargraves, and then declares that all the proceeds will go to War Relief, Inc. Zepp overhears Joe's announcement and tells the gang that he is planning to double-cross them. Later that evening, when Mr. Bryant arrives with the police to confront Joe about Hargraves' check and to demand a stop to the gambling, Joe hands him the envelope addressed to Hargraves and orders the proceeds totalled. In the cashier's cage, Joe is confronted by Zepp and the others, who threaten to expose him as a draft dodger unless he remains silent about the false bottoms in the cash boxes. After the War Relief workers leave the office with a paltry $812 retrieved from the boxes, Zepp unloads the bottoms, rolling the money in a newspaper. Aware that she has been cheated, Dorothy returns to the cage and demands the money. Joe, knowing that Zepp has a gun in his pocket pointed at her, slaps Dorothy unconscious and then slugs Zepp, who shoots Joe. Before the crowd can return, the wounded Joe kicks Zepp in the head, gathers the money and escapes. The next day, at the Bryant house, a distraught Dorothy is about to make a statement to the press when Swede arrives to deliver the bundle of money. Although Swede refuses to tell Dorothy where Joe is hiding, she tracks him down when she hears that the Fortuna has been turned into a medical ship and renamed the Briny Marlin . Racing to the docks, Dorothy arrives just in time to see Joe sail away. Although she begs him to let her join him, he refuses. Swede concludes his story by telling the watchman that after delivering the medical supplies, the ship was sunk and he and Joe enlisted in the Merchant Marine and are now home on leave. When Joe joins Swede at the docks, the watchman orders them to move their dinghy, which is tied up to the pier on which Dorothy is standing. The watchman suggests that they flip a coin to decide who will move it, and employing a two-headed coin, he tricks Joe into losing. As Joe begins to walk toward the boat, Dorothy sees him and the two embrace.