This is a parody is based on a British comic strip, and the film came off as another one of the James Bond spoofs that littered the screen in the 1960's (The Matt Helm series, the Dr. Goldfoot series, etc).
The movie is about superspy Modesty Blaise (Vitti), who can change her appearance just by snapping her fingers. She is hired by the British government to protect a shipment of diamonds, which international thief Gabriel (Bogarde) is after. Blaise only accepts the job if Willie Garvin (Stamp) is allowed to work with her. Film goes on its way from there.
Script is infuriating because it misses opportunity after opportunity for satire. It assumes that just because Blaise is a woman superspy, that alone is hilarious. Vitti does her best, and sounds like a smoky voiced Garbo, but the script leaves her high and dry. She gets most of her laughs from intonation, sight gags, and the glint in her eyes. Stamp is on the sidelines, although his appearance changes at will also. Bogarde as Gabriel is the funniest person in the film, whether he's refusing an egg because it's overcooked or reminding a potential killer that it's rude to point.
This one does have Bogarde, and Blaises' changes are spectacular, and so are the sets. There are setpieces that are homages to famous directors, which I found amusing. However, it just goes on too long for what little it is trying to do, there are too many dry spells without laughs, and Bogarde and company are off-screen for too long. Still worth a watch--maybe.