A dying master of the Poison Clan is training his final student, his sixth. Fearing the skills he taught to his previous students are being used to evil ends, he sends this student, Yan Tieh (played by Chiang Sheng), on a mission: Trace his former students, assess their moral standing (dispatching them if necessary), and protect the master's old partner. His partner became rich through the clan and he fears the old students will seek to steal the fortune.
During the course of his journey, Yan Tieh meets all five students. Alternatively referred to by their number (the order in which they were trained) or by their animal style, each student was taught only 1 of the 5 poison styles. Yan Tieh, number 6, was taught some of all 5 styles, but he had only 3 years of training so his master tells him "You must join up with one of the five, or you will have no chance of defeating them."
Number 2 (played by Wei Pei) is the Snake. He has a two pronged attack. He has the snake's mouth on one hand whereby using precise finger control he attacks the pressure points mimicking the poisonous effect of a snake bite. On his other hand is the stinging tail. He fights extremely well on his back. He and Number 1 trained at the same time. Nevertheless all students wore masks to hid their identities from each other. His color is silver.
Number 3 (played by Sun Chien) is the Scorpion. This style is all about striking. Hard. His kicks are like the stinging tail and his fists are like the pincer. He trained alone with the master and never met Number 1 or Number 2. He remains in the shadows for most of the movie. His color is either black or purple.
Number 4 (played by Philip Kwok) is the Lizard. The oldest of the fighters, he studied at the same time as Number 5. Remember that they all wore masks so none of them know the identities of the others. The lizard is an agile and nimble style. He can climb walls and fight with extreme dexterity from them. His color is gold.
Number 5 (played by Lo Meng) is the Toad. The movie's description of this style must be quoted verbatim and certain people may remember the line appearing a Wu-Tang Clan song. "The toad style is immensely strong and immune to nearly any weapon. When it's properly used, it's almost invincible." He can bend metal. His color is green as shown in the open sequence.
This movie was provided star-making roles for all six of its leads. In the years to come they became known as the Venom Mob, and would do many more films together as actors, stunt performers, and choreographers. Most of these films would also be directed by Chang Cheh.
This film provides examples of:
- Achilles' Heel:
- Toad is superhumanly tough, but once his ears get smashed, he loses his strength and is killed.
- Toward the end of the movie, Yang comes up with stratagems that he and Lizard can use against Centipede, Snake, and Scorpion, based on what he knows of their respective styles. Centipede is vulnerable to being attacked from different levels, so Yang attacks the legs while Lizard attacks the head. Snake, by contrast, is vulnerable if attacked from different sides, preventing him from using his hands in tandem. We never actually hear his tactic against Scorpion, but it's implied he has one.
- Animal Theme Naming: All the main characters/former students, except for Number 6, are given an animal name based off their Kung Fu style that mimics the animal.
- Creepy Centipedes: Centipede is an arrogant and brutal villain.
- Snakes Are Sinister: Downplayed. Snake is an elegant, cold-blooded villain, but he actually comes to realize that Being Evil Sucks and wants out.
- Scary Scorpions: Scorpion is the most mysterious of the bunch, with his true identity a secret until the climax of the movie. He is a cunning, elusive presence, playing the other four against each other.
- Lovable Lizard: Lizard is a charming and amiable policeman who tries to do the right thing.
- Amphibian Assault: Toad is a Nigh-Invulnerable Boisterous Bruiser. He and Lizard are the only good guys of the five.
- Animal-Themed Superbeing: Each of the titular Five Venoms qualifies as this. Numbers 1, 2 and 3 qualify as Type 2 - being Badass Normals who's fighting styles are vaguely based off of their animal namesakes - while 4 and 5 are Type 1 since they're styles are much less realistic, Lizard-style allowing Number 4 to cling to walls by his feet and Toad-style making Number 5 invincible.
- Arrogant Kung-Fu Guy: Most of them. Centipede is probably the most conventional case of this.
- Beard of Evil: Number 1, aka Centipede, has this. It's even lampshaded by the witness.
- Big Bad Duumvirate: At first it seems like Number 1 is set up to be the main Big Bad, but throughout the film, the balance of power among the antagonists' alliance sways.
- Boisterous Bruiser: Number 5, Brother Toad. He's a fun-loving, hard-drinking guy who is specifically described as "well-built".
- By-the-Book Cop: Constable Ma, partner of Constable Ho (the Lizard). Ma obeys the formalities of the law and encourages the falsely-arrested Toad to have faith that, if he's innocent, the courts will acquit him. Ultimately a subversion, however, as he's revealed to be a Dirty Cop and is, in fact, the Scorpion.
- Color-Coded for Your Convenience: As listed above, each of the Venoms is associated with a specific colour.
- The Chessmaster: Kao Chin, who was the Scorpion, is the one who orchestrated all the wrongdoings done, including multiple murders which includes the assassination of Liang Shen.
- The Coroner Doth Protest Too Much: After murdering Toad in his jail cell by effectively waterboarding him to death, the Dirty Cops hang up his body and announce that he committed suicide. Likewise, when Centipede and Snake are cleaning up loose ends by murdering the witness and policeman they bribed, they commit the murders with a long metal hook down the throat or up the nose, leaving no visible wound - although in this case, the coroner does confide to Lizard that he has found the internal wounds and knows exactly how the two men died, but he's afraid to say it publicly or he'll be killed too.
- Cowboy Cop: Constable Ho is introduced as a downplayed example of this, gratefully accepting the offer of some fresh fruit from a vendor even though, as a policeman, he's not allowed to accept gifts. When reminded of this by his By-the-Book Cop partner, Constable Ma, he insistently gives the vendor some money. In his dual identity of the Lizard, he also works outside the law to protect justice.
- Decoy Protagonist: It sways back and forth between Toad and the Sixth Student for a bit, but arguably the true hero is Lizard.
- Devil in Plain Sight: The Scorpion and Lizard are local constables, and the Snake is a rich nobleman. In the Lizard's case, he's actually a good guy.
- Dirty Cop: Basically all of them except Constable Ho Yuan-Hsin, who's actually Meng Tien-Hsia, the Lizard.
- The Dog Bites Back: Brother Snake turns on Brother Scorpion in the final fight after the latter attempted to kill Snake when he was fleeing; big mistake on the Scorpion's part...
- Final Battle-Induced Shirt Loss: Everyone wears open-fronted shirts, but Lizard is fully shirtless during the final battle.
- Hanging Judge: The local Judge.
- Heel Realization: At the start of the third act, Snake takes a brief moment to lament to Scorpion that while he doesn't actually want the treasure since he's already rich, he keeps killing to keep himself out of trouble and mentions he only joined the clan for the skills only, and asks when will it end. Scorpion laughs it off, saying that once started, it will never end.
- He Knows Too Much: The informant and the witness are both killed.
- Hong Kong Dub
- I Need a Freaking Drink: After Lizard returns from his trip to find that Centipede has been set free and Toad has been framed for the crime and killed, he immediately makes his way to a local inn and practically crawls inside one of their massive jars of wine.
- Iron Maiden: The film features an iron maiden variant with the victim's head exposed. Snake uses this to defeat Toad's "iron skin" power, but it only takes after Scorpion and Snake smash his ears and disable his ability.
- Kangaroo Court: In the murder trial, the judge is desperate to get a conviction quickly, not solve the case. Listening to the poisonous whisperings of Snake, the trial devolves into this rather quickly, ending in the conviction of Toad and the acquittal of Centipede. This was after Centipede was initially identified as the murderer, and he was apprehended thanks in no small part to Toad.
- Karma Houdini: The judge does not get any punishment but Yan Tieh does suggest it, only for Brother Lizard to say that his replacement could be worse.
- Lonely Rich Kid: Brother Snake, born into a rich family but entered the Poison clan just to master style of kung fu and is only started after the treasure because of loyalty to Centipede.
- Manipulative Bastard: Snake, who masterminds a way to turn the police against Toad, and get Constable Ho (whom he doesn't realize is Lizard, but does know is a friend of Toad) out of the way during the process.
- Martial Arts Movie: Obviously.
- Never One Murder: After the Yun massacre, Snake and Centipede have to frame Toad for their crimes and then commit two more murders to cover their tracks. See Rewarded as a Traitor Deserves below. Snake grows increasingly uncomfortable with all this, even wondering aloud where it will end. Scorpion simply tells him that it won't.
- Nigh-Invulnerable: The Toad can shrug off iron spikes and bend sheet metal with his bare fists. Just don't hit his ears.
- "Number of Objects" Title: The five people the protagonist has to find.
- Obfuscating Stupidity: Yan Tieh spends the bulk of the film pretending to be just a beggar to go under cover.
- Old Master: It is implied that the head of Five Venoms House is this, but downplayed due to the fact that he is dying at the beginning of the movie.
- A Pupil of Mine Until He Turned to Evil: The Poison Clan Teacher fears this to be the case for all his students except Number 6. Ultimately, it's only the first three who are evil.
- Perma-Stubble: Lizard sports a very fake-looking five o'clock shadow at all hours of the day. It never progresses to a full beard.
- Rapid-Fire Fisticuffs: Centipede style's specialty.
- Red Herring: The Scorpion is not the judge.
- Red Oni, Blue Oni: Number 1 (red) and Number 2 (blue) along with a similar relationship between Number 4 (blue) and Number 5 (red). Number 1 even wears red as his signature colour.
- Rewarded as a Traitor Deserves: After Centipede is freed, he and Snake murder the witness they threatened into lying, and the Dirty Cop they bribed, since they know they can't trust these guys to keep the secret.
- Secret Identity: Downplayed; most of the students used the name of their style to cloak their identity back when they were part of the Poison Clan. After they left, most of them either kept their name separate from their past or assumed a new identity after leaving the clan.
- The Centipede is Chang Hsiao-Tien; he doesn't really have much of a secret identity.
- The Snake is Chi Tung; he is back to being a rich nobleman like he originally was.
- The Scorpion, the most enigmatic of the three, is Kao Chin; he goes by the new identity of Chief Constable Ma Chou, and has been keeping Brother Lizard at bay the entire time to make sure everything went smoothly for himself and regarding the assassination of Liang Shen.
- The Lizard, is Meng Tien-Hsia; he goes by the new identity of Constable Ho Yuan-Hsin and is the one of the few good constables amongst them.
- The Toad, is Liang Shen; he is just a drinker at the tavern who acts an ally to Tien-Hsia.
- Shout-Out: In the scene where Yan and Lizard are practicing their strategies for how to defeat the bad guys' techniques, the background music is taken from Monty Python and the Holy Grail, of all things.
- The Red Mage: Yan Tieh, the last/sixth disciple, is essentially the kung fu version of this, knowing traces of all the techniques but not being an expert in any to stand against the others alone.
- Sacrificial Lion: Number 5.
- The Stool Pigeon: Wong Fa, who witnessed the murders at the Yun residence and identifies Centipede as the killer, is later intimidated into changing his story to implicate the innocent Toad.
- Sixth Ranger: The Hero, Yan Tieh, is this.
- Token Good Teammate: Meng Tien-Hsia, the practitioner of the Lizard Style, is the only one with a sense of justice and who used his skills afterwards for good despite his past. Toad could be called a downplayed example - while basically an okay guy, he doesn't have the heroic drive that Lizard has.
- Too Awesome to Use: Non-item example but Brother Toad is especially frustrated that he has to pretend to just be a random strong man and keep his true skills in secret. It's due to being one of the Venoms that a signature move set is such a revealing calling card.
- Torture Always Works: To both Centipede and Toad during the murder trial. Neither of the tough guys actually break under torture—but they're both really anxious not to undergo it again.
- Totally Radical: According to at least one version of the English subtitles, Snake's full title is "Snake Spirit Dude". This is only referred to once, then never mentioned again.
- Wall Crawl: A Lizard style specialty. He can even casually stroll up walls and hang out there as long as he wants.
- What Measure Is a Non-Cute?: The Venoms associated with the cuter animals - Lizard and Toad - are good guys, while those associated with scarier animals - Centipede, Snake, and Scorpion - are evil.
- You Are Number 6: The Deadly Venoms are often referred to by the order in which they were trained, though the movie's use of the trope lacks the dehumanizing implications it often has. Yan Tieh is, indeed, Number Six.