True Believer (1989)

Jaded lawyer Eddie Dodd (James Woods), a well-regarded activist in the 1960s whose moment has long passed, now smokes marijuana and defends drug dealers who pay in cash. Recent law graduate Roger Baron (Robert Downey Jr.) becomes Dodd's apprentice, hoping to learn from him. When an agitated mother walks in insisting her son is innocent of the murder he was jailed for eight years ago, idealistic Roger prods Eddie to take the case, and the pair uncovers a huge conspiracy that endangers them both.