Smuggler's Cove (1948)

"They're SLY SPIES...In a Harum-Scarem Adventure!!"

Slip and Sach are working as cleaners in a high rise building. They enter an office to clean it when a messenger hears them use Slip's given name, Terrance Mahoney. The messenger has a letter for "Terrance Mahonoey, Esq." and mistakenly delivers it to Slip. The letter informs Slip that he has inherited a mansion in Long Island. The boys then make their way to the mansion and find that it is inhabited by diamond smugglers. The real owner of the house shows up and helps save the day and defeat the smugglers and gives the boys the house as a reward.