Explain the lesson George learned. "Let George Do it" by Della Johnson

At the beginning of the Second World War, before Germany invaded Norway, a ukulele player in a British dance band playing at a Bergen hotel, is found dead during a radio broadcast of the band's show. It turns out he was a British agent keeping an eye on the band leader, Mark Mendes (Garry Marsh), who is suspected of being a German agent passing on information about British shipping to German U-boats, using a code concealed in the radio broadcasts.

When Mendes calls a musician's agent in London for a replacement, British Intelligence tries to send another agent in his place. However, through a series of mistakes in a blacked out Dover, ukulele player George Hepplewhite (George Formby), who is on his way to Blackpool, is put on the boat to Bergen instead of the new agent. When he arrives, the receptionist at the hotel, Mary Wilson (Phyllis Calvert), who is another British agent, makes contact but eventually realises the mistake. George, however, is totally unaware and starts working with the band, although Mendes is suspicious of him. Eventually Mary tells George what is going on, and together they manage to find what the code is and alert the British Navy.