When three boys were brutally murdered in the small community of West Memphis in Arkansas in 1993, the perpetrators were quickly identified in the deeply religious city: three teenagers who were said to have a connection to a Satanic cult. The so-called "West Memphis Three" are being made short work of. Two of them are sentenced to life imprisonment, their alleged leader to death – despite contradictory evidence. Private investigator Ron Lax (Colin Firth) has doubts about the verdict and soon gets an ally from an unexpected side: the mother (Reese Witherspoon) of one of the murdered children also doesn't believe in the guilt of the teenagers. But the identity of the real perpetrator lies in the dark shadow of the supposed truth...