In Iberia Parish, Detective Dave Robicheaux (Tommy Lee Jones) is investigating the murder of a young woman and has a chance encounter with a pair of Hollywood stars Elrod Sykes (Peter Sarsgaard) and his girlfriend Kelly Drummond (Kelly Macdonald) who are in the small town to film a Civil War film. Due to his erratic driving, Dave determines Elrod is driving his Lamborghini drunk and sets to arrest him. Elrod, objecting to being sent to jail tells Dave of a decayed corpse that he and Kelly had found up in the swamp.When Dave goes to investigate he remembers a murder he had witnessed as a teenager where a chained prisoner was shot in the swamp and disappeared into the bog. The discovery opens a string of events that ties to several murders in that area that had occurred recently mostly to young runaways and prostitutes. The clues seem to point to a former friend of Dave's, Julius "Baby Feet" Balboni (John Goodman) whose ties with the mafia had caused the two to drift apart and become strained enemies. Julius denies knowing the prostitute whose murder is being investigated. However his story does not corroborate, leading Dave to suspect more to the story.Meanwhile, the discovery of a second body prompts the FBI to become involved in the case, and Dave is partnered with an agent called Rosie Gomez (Justina Machado) whose insight into the case gains Dave's respect and the pair team up to solve the case. Dave attends a birthday party for Michael Goldman (John Sayles) and after drinking a Dr. Pepper, becomes terribly uncoordinated during his drive home and crashes his truck, sending him off in a daze to the forest where he encounters a camp of Confederate soldiers, and their commanding officer General John Bell Hood (Levon Helm) who wishes to help Dave with his journey to solve these murders. When he awakens from his daze, he learns from Gomez that his drink had been laced with LSD.Later Dave's partner Lou Girard (Pruitt Taylor Vince), is found dead, apparently by shooting himself with a shotgun. Dave's queries to why Lou shot himself with the shotgun out of depression despite the easier handgun, are shrugged off that he was drunk and didn't know better. After the other officers leave the scene Dave takes the pistol strapped to Lou's ankle. Later Elrod drunkenly takes a boat out on a run of the swamp with Kelly, calling Dave when the pair get the boat engines caught in crab nets. Dave gives Kelly his coat as it is pouring down with rain, and a mysterious gunman shoots her in the chest, mistaking her for him. General Hood offers advice regarding the murders recently and Dave moves forward, shaking off the feelings of guilt over Kelly's death. Elrod moves in for a while so Dave can be an A.A. buddy for him. Later a pimp Cholo Manelli (Julio Cedillo) visits Dave and corroborates a suspect, Murphy Doucet (Bernard Hocke), who with his partner Twinkie Lemoyne (Ned Beatty) are responsible for the death of DeWitt Prejean, the skeleton found in the swamp. Dave arrests Doucet who gets out on bail and kidnaps Daves daughter Alafair (Alana Locke). Gomez and Dave force Baby Feet into telling them about a campsite Doucet owns and the pair head there to capture or kill him. Gomez is startled by Doucet bursting out of an outhouse and instinctively shoots him. Dave plants Lou's pistol in Doucet's hand to ensure that Gomez is cleared of any charges of murdering him. They free Alafair and return home.Dave, who had stopped seeing visions of General Hood after the case was solved determines that he was a figment of his imagination, a lingering spirit to help him through the most difficult case of his life. He moves on with his life, while Baby Feet, according to Dave was arrested for an issue that no one would have suspected, not as a mafia criminal, but as a tax dodger. Elrod moves on with his life, leaving his alcohol addiction behind; he gives Alafair a small role in the Civil War film, and claims that she alone was responsible for his recovery. As the movie ends, Alafair is looking through a book on the Civil War when she comes across a photograph of General John Bell Hood and his group of soldiers. She begins to turn the page but turns back and as we see a close up of the old photo; standing in the back among the Confederate soldiers, is Dave Robicheaux.
Output: Question: What substance is put in Dave's drink?, Answer: LSD