The gorgeous Margot supports her aged father by seducing men on trains, slipping them a Mickey Finn (a beso de sueño) and robbing them of money and jewelry. One night her victim is a currency smuggler taking 100 million pesetas out of Spain. He's being watched by a cop and by a burned-out alcoholic, Salvatierra, who does occasional jobs for a corrupt banker; they are quickly on Margot's trail. The cop suspects Salvatierra of working with Margot, but Salvatierra has his own agenda. He becomes Margot's protector; is it for his own good or for hers as well? And what are these feelings that develop between the two of them? Where will the money end up?