Former Louisiana State CID partners Martin Hart and Rustin Cohle give separate statements to a pair of investigators about the murder of a prostitute, Dora Lange, 17 years earlier. As they look back, details of the crime, replete with occult overtones, are accompanied by insights into the detectives’ volatile partnership and personal lives.

A hidden image at the burned-out church leads Cohle and Hart to Joel Theriot, a tent-revival minister whose parishioners finger a scarred “tall man” seen with Dora Lange. Brought in for interrogation, a sex offender matching the description is quickly dismissed by Cohle, despite offering a confession. Hart gets sidetracked after Maggie sets Cohle up with a friend at a C&W bar. Looking to establish a pattern of murder, Cohle pores over old case files, finding a connection with a woman assumed to have drowned years earlier.

Hart and Cohle hunt for their newly identified suspect, Reggie Ledoux, a meth cooker who shared a cell with Dora Lange's husband and recently skipped parole. As Hart's personal life collapses around him, Cohle immerses himself in an old criminal identity from his narco days, contacting an East-Texas biker gang known to deal with their primary suspect.

A violent denouement in the forest clears the Dora Lange case and turns Cohle and Hart into local heroes. Each man settles into a healthier rhythm of living as Hart returns to his family, and Cohle starts a relationship while gaining a reputation as a closer in interrogations. As time passes and his daughters grow older, Hart faces new tensions and temptations, and Cohle learns from a double-murder suspect that there could be much more to an old case than he'd once thought. In 2012, Gilbough and Papania put their cards on the table, presenting new intelligence that threatens Cohle and causes Hart to reassess everything he thought he knew about his former partner.

Maggie reveals Cohle's activities in 2002, when his relationship with Hart fractured and he quit the force.

Hart and Cohle call a truce to investigate a series of disappearances that may be related to the Dora Lange murder and the Tuttle family.