Though Howard Marks (Rhys Ifans) aka Mr. Nice is able to dodge jail on two separate occasions due to luck and his past as a government informant, Marks is finally arrested in an interagency sting. Marks refuses to testify against any of his fellow business partners, but they testify against him. In 1988, he is sentenced to 25 years in federal prison and must serve it in Terre Haute in Indiana, far away from his wife Judy (Chloe Sevigny) and his four children.
Despite his surroundings, he is well respected due to his education and his unwillingness to rat on his business partners. He becomes a teacher and jailhouse lawyer, even getting some convictions overturned. Seven years later, at a parole hearing, Marks feels he has no shot of getting it granted. However, several inmates testify on his behalf, noting the various ways, such as furthering their education, that Marks has helped them. The parole board also notes that the judge's recommendation that Marks serve his time in prison in the UK (where he could be closer to his children) was ignored by the DEA and thus has made his time more "cruel and severe" than warranted. As thus, they will grant him parole after 7 years in prison.
Marks returns home and is tearfully reunited with his family. He later becomes a best selling author, speaker, and cult hero.