The strange case has been made through studies that kids will laugh when presented with something out of place, like a funny face, if the face is made by someone with whom they are acquainted, but they will repel if it's presented by a stranger. This conveys that our reactions to inconsistencies, oddities, unanticipated discrepancies with normalcy and established ranks will differ in terms of particular circumstances. If the incongruity happens in a context where it's threatening, it'll dispose us toward a threatened reaction. This is maybe the seed of the horror genre. On the other hand, if the context is one that is distinguished as non-threatening, where the possibility of hurt and fear has been withheld, the scenarios are opportune for humor.
We follow the attempts of Sherlock Holmes, Dr. Watson and various governments to stop all civilization from being destroyed, but everyone is too terminally stupid or apathetic to be successful at it. We need not worry about the targets of all the brutality and cruelty in blacker realms of comedy, including slapstick, because they're not completely human.
It's an accelerated, often hilarious jaunt that heckles at just about everything mystery, espionage or potboiler in English and American media. Holmes, Bond, Columbo, etc., little more than a vaudeville act in breadth and elaboration. The peak of this film is Arthur Lowe as the guileless, blundering Watson, his stupidity and listlessness always counterblowing Cleese's temperamental ingenuity.