Terence Hill is a movie stunt man. Bud Spencer is jazz saxophonist. They are also exact doubles of two Brazilian cousins who are trying to sign a deal, but whose lives are being threatened. The first two are offered a million dollars each to impersonate the latter two for a week, and an additional half million each if they can figure out who's doing it. So they fly down to Brazil and turn the staid, stuffy, effete lives of their doubles upside down.
It's certainly not a novel idea for a comedy movie, so the question is how Hill & Spencer's comedy character make use of situations, as well as the amusement of seeing them playing characters so far from their wheelhouses. It's all very well handled, with lots of the usual low-brow gags and boisterous fight scenes with thugs; Hill & Spencer are, of course, invariably victorious in these.
This sort of slapstick fell out of fashion long ago. For those of us who enjoy old-time comedy, however, will find a lot to take pleasure in their movies in general, and this one in particular.