Dardo, a Robin Hood-like figure, and his loyal followers use a Roman ruin in Medieval Lombardy as their headquarters as they conduct an insurgency against their Hessian conquerors.
When a neutral Danish merchant ship is forced to put into port after trying to evade British wartime contraband control, its captain becomes involved in a beautiful British Naval Intelligent agent's efforts to capture a group of German spies operating from a London cinema.
Lots of slogans such as "Be like Dad, Keep Mum" and "Keep it under your Hat" are visible on the walls in various scenes to reinforce the plot of this British wartime movie illustrating how gossipy talk can result in unknowingly giving valuable information to Nazi spies.
A professor teaching at a correspondence school discovers that a Nazi agent is trying to prevent a trade treaty being signed between England and South America.
