This is one nasty old-school chop-socky.
Tien Peng approaches this film with the decision to make his Chinese spy in the Japanese-occupied territories as ruthless as any Western "anti-hero". So of course he comes up with an anti-hero that is the worst imaginable.
I mean, the Japanese guard was certainly despicable - but what "hero" could be so cruel as to force the guard to watch the guard's dog being cooked and eaten - before killing the guard with his own sword anyway? I'd like to say the hero kills first and then asks questions later - but he never bothers to ask any questions.
If it weren't for a great sense of timing - surprising from a director so young - this would be almost intolerably vicious. Be prepared for one of the roughest, most violent fight films of its era, utterly unredeemed with any humor or romance, and where the Chinese hero is the hero simply because the Japanese are bad-guys.