Eli Snedeker (George Tobias) runs his diamond mine with a ruthless iron fist, skillfully engineered by John Gamble (George Brent). Tiring of Snedeker's sadistic treatment and advances from Snedeker's wife, Delia (Lee Patrick), Gamble quashes Snedeker's attempt to buy out Roger Smythe's (Miles Mander) neighboring claim and convinces Smythe to take him on as a partner. Smythe's bad fortunes turn around thanks to Gamble's efforts, and the two discover the fabulous Star of Africa, a diamond of astonishing size and beauty. As Gamble and Smythe make plans to sell their diamonds and rendezvous in Alexandria, Snedeker strikes, leaving Gamble framed for murder. Disguising himself as wealthy financier John Bradley, Gamble tracks down Smythe's daughter, Katharine (Brenda Marshall), to give her the Star of Africa. There's only one problem: The Star of Africa is Exhibit A in the murder case against John Gamble!