Charles Bronson is old and needs to make a few bucks to pay for his funeral in 1985.
Paul Kersey (Bronson) is a vigilante and is hired by a lazy cop to go clean up the streets. So Paul leaves valuable things lying around so that someone can steal it and he can kill them for it. Pretty simple.
The first 10 minutes are enough premise to give Paul an excuse to murder pretty much everyone. He gives zero fucks and kills everyone. It is hilarious and it doesnt pause. The last one has a bazooka at point blank range.