What follows this plot description includes loads of suspicion, flying swordfights, swirling silks, gory murder and wild mysticism. In short, this film is made in the classic late 70's wu'xia tradition, and is a great actioner, though ultimately very depressing, because only one (or perhaps two) of the characters survive.
And if you need another reason to watch, Cynthia Khan is given the full glamour treatment. (I think the producers gave her a Joey Wong makeover !). She's never looked lovelier.