It's basically a British version of Death Wish.
Harry Brown, a pensioner living alone in a bad part of London, sees society around him falling apart into drugs, violence, and barbarism. But he does nothing, tending to his own affairs, until his best friend is murdered. Then this old Royal Marine turns into a vigilante.
Michael Caine does a superb job in this better written, higher production take on the Death Wish story. It's as much social commentary as it is an action movie, as urban youths are depicted in nearly subhuman form and the police are either useless or helpless to prevent or punish random criminal violence.
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