The London Man (1943)

Maloin, a maritime station guard, spends his nights at the port signal box. One night, he becomes the witness of a murder: for a simple suitcase smuggled, the altercation between the two men turns to drama. While the first falls and drowns, the second flees. Maloin, instead of warning the police, decides to dive in and recover the suitcase...which contains more than 3 million in small denominations! That's when the trouble begins...