This is the story of a fairly ordinary American businessman with a loving wife and family, who ends up in jail in the company of hardened criminals. In order to survive, he soon emulates the other inmates, resorting to violence when he needs to.
There are implausible details in the story, more particularly towards the end, in my view, but it is a very good film that will stay with you, because of the depiction of prison life -- the violence, the gangs, and the code of honour among inmates. You realise what the culture in prisons is and how they operate: it's like a punch in the face and a kick in the stomach. It comes across as very realistic, in terms of US prisons, at any rate (but I suspect conditions are similar in many British prisons, where we hear the level of violence is growing all the time).
So, I recommend this movie, if you have the stomach for this kind of storyline, which is dark but compelling.
Spoiler Alert: Mild mannered Businessman goes to prison for Vehicular Manslaughter , ends up Tattooed up to the eyeballs, leader of a White Supremacist gang and hardened killer who it turns out can stab people without flinching or seemingly caring about it.
I guess inside every happily married middle class Businessman in California there's a Nazi Gang leading Psycho waiting to get out!
Absolutely ridiculous storyline!
Just about recommend this. Not particularly original but it is pacey and efficiently made. Fine acting generally especially jamie Lannister but you could try something better such as the mighty tv series Oz or A Prophet.