A woman loves a doctor going away to experiment; so she marries his brother but regrets it and tries to win back the doctor experimenting.
A tropical disease has killed 9,000 workers, and playboy Chris Claibourne (Robert Taylor) plans to go with Professor Fahrenheim (Jean Hersholt) on an expedition. Rita Wilson (Barbara Stanwyck) wins at roulette. Fish-Eye (Joseph Calleia) pays her and asks her to send customers for 10%. Chris lost, and Rita buys him a drink. They flirt and stay out all night and then play for ten days. Chris has one day before he leaves, and Rita cries. Chris agrees to stay; but Chris is taken to Fish-Eye to pay his $5,000 debt. Chris writes a check but needs money or it's prison. His brother Tom Claibourne (John Eldredge) will loan him the money, but Chris must go on the expedition. Rita gets angry and walks out. She goes to Fish-Eye and offers to help in order to pay the debt. Rita tells Tom she paid Fish-Eye. Tom dances with her and says he is engaged.
In the tropics Chris gets no mail. Fahrenheim says they are using the process of elimination, but Chris says he is leaving. Tom is telling his father (Samuel S. Hinds) his mind is not on his work since he broke his engagement when Chris barges in. Tom tells him he married Rita; but she left him after the wedding. Tom tells Chris that Rita paid his debt. Chris finds Rita and asks why she married Tom. Rita says she got even. Chris has only $711, but he rolls dice. Fish-Eye tells Rita to make Chris use his dice; but Chris stops while ahead $5300 and pays off Rita. She is ashamed and wants a divorce. Chris asks her to go with him on the boat.
In the tropics Rita tells Chris he is working too hard. They wait for news of her divorce, and he kisses her. Charlie is dying and says it is ticks. Chris takes a tick from a goat and makes a rat sick. Then he makes serum from the goat's blood and cures the rat; but Charlie dies. Fahrenheim says the serum was too late. Chris gets a letter that Tom's divorce was granted. Chris gives Rita money and tells her to leave. Rita tells Chris she loves him, but he is blinded by arrogance. Captain Tanetz revokes Chris's license. Fahrenheim and Chris are warned that if a native dies of their treatment, they will be indicted for murder. Rita offers herself to test the serum; but Chris declines it as too risky. Rita hears of a test on Chris and tries to get authorities to stop it. Fahrenheim delays Chris by breaking the serum bottle. Rita arrives and gives herself a shot of disease. Fahrenheim and Chris make more serum, and Chris gives it to her. In the final scene on the boat Chris gives the credit to his wife Rita.
Rita messes up four lives by marrying out of spite; but eventually her self-sacrificing to help the important work of Chris and Fahrenheim helps their beneficial work.