Master armourer Tomás has young wife Alena, of whom he is very jealous. One day the ruler of town sees Alena and decides to win her over for himself. To get a free hand for his love affairs, he sends Master Tomás to acquire more skills in Flanders. Jealous husband does not know how to secure fidelity of his beautiful wife while he is away, and finally accepts aid of the devil, to whom he signs his soul as a reward. Devil in the disguise of Master Ondrej works in Tomás's workshop and protects Alena against various courtiers and the ruler of town. But finally he falls in love with Alena himself and becomes her lover.