Adapted from David Garth's novel, after their father is dishonorably discharged, four brothers investigate his murder to clear his name.
In India Col. Loring Leigh (C. Aubrey Smith) is tried for a massacre after a gate is left unguarded, and he is discharged. He sends cables to his sons Rodney Leigh (William Henry), lawyer Wyatt Leigh (George Sanders), womanizer Christopher Leigh (David Niven), and diplomat Geoffrey Leigh (Richard Greene). Wyatt says the evidence is against him; but their father says a munitions syndicate sold weapons to the revolt. The four hear a shot and find their father dead with his papers missing. Wyatt suspects murder, but it is called suicide. Geoff finds Lynn Cherrington (Loretta Young) also came from Washington. Captain Drake calls Geoff and says he is being followed. Geoff finds Drake dead in a taxi. Lynn learns that Geoff is going to Buenos Aires and plans to beat him there.
Wyatt and Rodney investigate in India, and trooper Mulcahay (Barry Fitzgeral) is shot in the arm. Rodney finds a pistol with the name chiseled off, and Wyatt calls Geoff about the gun. On a yacht Lynn cajoles Douglas Loveland (Reginald Denny). Geoff objects, and Lynn quarrels with him. On an island, where guns supply a revolt, Lynn and Loveland follow General Torres (J. Edward Bromberg) to the guns and rebels. General Sebastian (John Carradine) takes Torres to a wall and has him shot. Rebels shout and are massacred with machine guns, but Lynn and Loveland escape. A man appeals to Loveland, who denies knowing him. Geoff intervenes and is put in jail with the man who tells Geoff of the arms deals. Lynn gets them out; Geoff says he was jealous and is in love with her. Geoff and Chris realize that Atlas Arms sold guns in both places. They accuse Loveland of perjury against their father. Loveland admits forging the order but is killed before he can say who killed their father.
Geoff and Chris question Furnoy (Alan Hale), who says his business is rubber. Furnoy tells Lynn that her father is president of Atlas Arms. Geoff and Chris learn that Lynn is gone, and Wyatt calls them that her father is in Alexandria. Lynn calls on her father, Martin Cherrington (Berton Churchill), who admits he owns Atlas Arms. Lynn says she will fight him. Wyatt and Rodney welcome Geoff and Chris to Alexandria; but Geoff won't let Lynn explain. Lynn helps Wyatt and Rodney to see her father. Cherrington says he does not approve of murder and promises to sell his Atlas stock, but they should see Furnoy. The four swim to Furnoy's yacht, tie up the captain, grab the secretary, and make Furnoy confess. In the final scene at London the four brothers restore the honor of the Leigh name.
This mystery contains occasional comments against the nefarious arms business that causes such misery but in its quest for family honor mostly ignores British imperialism. Lynn is a liberated woman acting independently though her motivation is primarily to get her man.