Classic 1978 Shaw Brothers kung fu enfused with the message that crippled people kick serious, serious ass.
The bad guy is a monumental jerk, as his response to having his wife killed and son getting his arms chopped off... is to build his son iron hands and go around crippling people. Clearly, they are acting out their unresolved issues... plus, it's a totally dick move. You get your hands cut off, so you go around cutting off other people's hands? WTF, man!
In their ridiculous lack of self-awareness, evil father and son blind a guy with a devastating eye-poke, mute a guy by making him drink poison, chop off a guy's legs for walking carelessly, and turn a guy into an idiot by squeezing his head really hard.
Again, the son... who got his hands chopped off in random violence... goes around committing ramdom violence by crippling people in various ways. Apparently therapy was not a widely practiced martial art in those days.
Of course the 4 crippled guys band together, learn a bunch of ability-specific kung-fu, and come back to wreak vengeance on the evil bastards.
Excellent all around... great setup, great action, and the right level of horrific violence and bizzare concept to make this one of the best ever old-school kung fu flicks.
This movie also stars the "Venom Mob," or all those guys who were in Five Deadly Venoms... childhood friends who went on to make a bunch of movies together. Apparently they all tooks turns directing and being the star in a series of movies. This is one of the most excellent of those films.