AllMovie

Entering a bank to make a small withdrawal, Herman (Fred Gwynne) and Grandpa (Al Lewis) are mistaken for a pair of bank robbers who wear "monster" masks when pulling off their heists. As a result, the terrified teller hands over $18,000 to the hapless duo--and when Herman finally realizes that a mistake has been made, he regards it as his civic duty to return the money immediately. Unfortunately he makes this decision late night, long after the bank has closed, meaning that Herman and Grandpa are going to have to stage a break-in to prove their honesty!