Bret Maverick falls for a soft-spoken girl, Modesty Blaine (Mona Freeman). They enter into a partnership — to sell cats to a mining camp overrun by rats. But rumor has it that most men lose either their lives or their money when dealing with this young beauty. However, Bret stands to lose both his life and his money, so he plots to save both.

Bret is one of the seven owners of a Riverboat who start down the Mississippi for Memphis to sell the broken-down craft, but soon in a deadly game of 10 Little Indians one owner after another is found mysteriously dead. It becomes apparent that if the boat does reach Memphis, it's almost certain it will have but one owner.