Castle Falls follows the story of a janitor named Donal (played by Dolph Lundgren) who stumbles upon a large sum of money hidden in a luxury condominium that is set to be demolished. The money belongs to rival gangs who have been seeking it out for years. When they find out that Donal has the money, they set out to retrieve it.
Donal is a former military man who suffers from PTSD and struggles to make ends meet. He sees the money as his ticket to a better life, but he soon realizes he has put himself in danger by taking it. The gangs stop at nothing to get their hands on the cash, including kidnapping Donal's daughter.
The condominium building becomes a battleground as the gangs fight to take control of the money. Donal is forced to fight back, using his military training and wits to stay one step ahead of his adversaries.
As the building crumbles around them, the characters engage in an intense game of cat and mouse, fighting for survival and the chance to claim the money. In the end, Donal emerges victorious, using the money to start a new life with his family.