Christian Bale plays John Preston, a Grammaton Cleric whose job is to enforce the law regarding "sense crimes" in Libria, a post-apocalyptic city-state where the citizens are all required to take Prodium to suppress their emotions, since emotions lead to hate and violence, which leads to war, etc. In practice, anything that stimulates emotion is bad, and one of the things the Clerics do is lead sweeps into the "Hinters" outside the city to seek out and destroy those who reject Father's doped utopia, burning their artworks, souvenirs, music, and even shooting their dogs. The Grammaton Clerics also serve as a KGB for the regime, turning in even their own comrades for sense crimes, which leads to problems for Preston as he becomes increasingly subject to emotion the longer he stays off the Prodium.
There is an Underground, but it's pretty ineffectual and can only manage occasional bombings of the Prodium distribution points...until Preston, whose descent into rebellion begins with an accidental failure to take his morning shot of Prodium, finds them and becomes their greatest weapon.
The movie has a pretty sizable cult following, and certainly deserves to be considered in the same class as The Matrix, Gattaca, and other dystopian flicks. Recommended.
*Yes, Emily Watson is cute, but she doesn't get nearly enough screen time and never dresses in PVC. That's what the servants of the regime get to wear, and neither they nor it are sexy.