Expert mountain-guide Maciste lives in the Dolomites at the Three Crosses Pass; he dotes on his young nephew Hans, the illegitimate son of his sister, who died of a broken heart for the dishonour of being seduced and abandoned. Maciste’s bitter rival is the sinister Schultz, a smuggler in search of easy money who teams up with two adventurers: Müller and the mysterious Vanna Dardos. Schultz’s plan is to steal the design for a revolutionary aviation project that engineer Riccardo Ewert is finishing in the peace and quiet of his mountain chalet. Vanna, however, is not the only woman who is interested in the engineer, as he has also caught the attention of beautiful English painter Maud Fair, who is holidaying in a luxury hotel and is secretly in love with him. Absorbed in her attempt to seduce the engineer, Vanna fails to notice that a police inspector is on her trail. Ewert is devastated when he finds out that the alluring woman being investigated for espionage is none other than the wife who had an affair and left him years before. In the meantime, Maud, aided by Maciste, manages to fend off Müller’s violent advances. Alerted by the inspector, Ewert pretends to fall into Vanna’s trap so that she can be arrested. Seeing all is lost, Müller and Schultz try to escape along Giant Pass, but they die in a blizzard; Vanna is forced to flee. At long last, Maud can be with the man she loves.