Henri Decoin - L’homme de Londres AKA The London Man (1943)

Synopsis (possible spoilers):

‘A port swathed in dense fog sees the coming and going of boats all day. During the night, Maloin is the man who controls the trains that transport goods to and from the port. One evening, he sees a man get off the boat from London and hand his suitcase to another man who has been waiting for him. Unaware that Maloin is watching them, the two men get into a fight, which ends with one of them falling into the water with the suitcase. As the other man flees, Maloin dives in and recovers the suitcase. To his surprise, it is full of money. Back home, he tells nothing about this to his wife and daughter but hints that they will soon have a better life. What follows will prove otherwise…’
– Willems Henri