Fidibus.

Kalle, a nice middleclass kid, who because of a debt and old friendship ends up as a 'fidibus', a gofer, for the hash baron Paten. But only until Paten is anything but innocently jailed and asks Kalle to mind the store while he is gone. No one touches Paten's money, Paten's car or, least of all, Paten's girl, Saby, who is dumber than water.