Sulfur Springs

Sulfur Springs follows Cork O'Connor, the former sheriff of Tamarack County, Minnesota, and now a private investigator, as he and his new wife travel to the Arizona borderlands to find her missing son.

Cork, a man shaped by loss whose father and first wife were both killed by violence, has recently married Rainy Bisonette, a Lac Courte Oreilles Ojibwe and a Mide, or healer, of the Grand Medicine Society, an Ojibwe spiritual tradition. On the evening of July 4th, Rainy receives a garbled voice message from her son Peter, who lives in Cadiz, Arizona, where he completed drug rehabilitation and became a substance abuse counselor. In the message, Peter appears to say he killed someone named Rodriguez and that people will be looking for him. Repeated attempts to reach him fail. Before flying to Arizona, they seek counsel from Rainy's great-uncle Henry Meloux, an ancient Mide living in isolation on Crow Point, who advises Rainy not to feed Peter's fear with her own. Rainy also reveals that Peter is not the only Bisonette who has killed a man in Arizona but refuses to explain, signaling that her past holds significant secrets.

In Coronado County, Arizona, local law enforcement has no record of Peter. At the Norman Goodman Center for Recovery, director Jeanette Saunders reveals Peter was let go over a year ago after showing signs of possible relapse and directs them to Frank and Jayne Harris, vineyard owners who hired Peter afterward. In Sulfur Springs, a small border town where Peter receives his mail, every resident denies knowing him. Cork senses they are lying. At the Harrises' winery, the couple confirms Peter works for them but did not show up that day. Robert "Jocko" Wieman, an elderly former crop duster who works for the Harrises, warns Cork cryptically that Peter is in real trouble.

Pastor Michelle Abbott, a retired Marine intelligence officer turned Methodist minister, listens to Peter's message and identifies the word Lagarto (Lizard), the nickname of Carlos Rodriguez, head of Las Calaveras (the Skulls), a cartel operating in northern Mexico. That night, Cork catches Rainy making a secretive phone call; she claims it was to her daughter, but Cork senses she is lying. The next morning, their rented Jeep Cherokee explodes when Cork uses a remote starter. Both survive the car bomb unharmed but are forced from their inn. Michelle offers them the church parsonage and her truck, explaining that a war rages along the border involving cartels, Border Patrol, vigilante groups called White Horse, undocumented refugees, and humanitarian organizations.

Nikki Edwards, a local radio DJ and Peter's close friend, reveals that Peter leads Los Angeles del Desierto (Desert Angels), a secret humanitarian organization that guides undocumented women and children safely across the border. Peter uses his Marine reconnaissance training to evade Border Patrol and cartel enforcers, while Nikki broadcasts rendezvous coordinates embedded in her nightly radio show. She gives Cork a contact for someone called Old Turtle, Peter's emergency contact, and warns that White Horse vigilantes also target the Desert Angels.

Cork identifies Old Turtle as Jocko, who reveals he usually flies Peter to remote desert landing strips for border crossings. Peter failed to appear for a prearranged pickup after his call to Rainy. During a search flight over the Santa Margarita Mountains, Cork spots deliberate mirror flashes from a narrow fold in the terrain, but a nearby helicopter causes the signaling to stop. When they return, Rainy is gone from Jocko's ranch, her phone abandoned in blood-soaked grass. Cork fears the worst.

That night, Cork discovers Rainy alive in the church, accompanied by Gilberto Mondragón, her ex-husband and the father of her children, a fact Rainy never disclosed. Mondragón, from a powerful Mexican family with cartel connections, had been watching from a distance and killed Rainy's assailant with a sniper rifle before taking her into hiding. Rainy reveals her full history: She married Mondragón at eighteen and had two children, but when his family drew him back into their criminal enterprise, a family associate tried to kill her. Rainy shot the man dead and fled to Wisconsin. Mondragón did not contest the divorce but later funded Peter's rehabilitation. He insists on keeping Rainy hidden, and Cork reluctantly agrees, struggling with jealousy.

Cork is ambushed on the Old Douglas Road by armed Las Calaveras gunmen demanding Peter's location and wounds two with a Winchester rifle before law enforcement arrives. Later, members of White Horse beat and torture him at the parsonage. Cork identifies Marian Brown, the mayor of Sulfur Springs, by her distinctive perfume and suspects Officer Mike Sanchez is also involved. Mondragón shoots through the window, wounding the group's leader, Royal Diggs, and scattering the attackers. Cork, Rainy, and Mondragón then reach the Lulabelle Mine in the Santa Margarita Mountains, where they find blood but no Peter. Rodriguez's men ambush them, and Mondragón's paramilitary force intervenes. A captured fighter reveals that Carlos Rodriguez was badly wounded in a recent firefight and that his eldest son Miguel did not return.

With help from Sylvester, an old prospector who has been assisting Peter in filing claims on abandoned mines used as refugee sanctuaries, Cork locates the Jesus Lode Mine. Inside, he finds Peter alive but wounded in the thigh, sheltering with 11 Guatemalan refugees. Peter explains that someone leaked his rendezvous coordinates to Rodriguez, who ambushed them at the border. Unknown attackers also fired on Rodriguez's men during the chaos. Peter led the refugees through the desert on foot to safety. Cork bonds with Juan, a 12-year-old Guatemalan boy whose family was murdered, who dreams of pitching for the Dodgers.

After getting Peter medical treatment in Arivaca, Cork pieces together the full conspiracy. He shares intelligence with Border Patrol Agent Jamie Sprangers and subdues Diggs in the church. Marian Brown is then found murdered. At the El Dorado Mine, Sanchez lures Cork into a trap on Rodriguez's orders, but Sylvester, positioned on high ground, saves Cork's life with a rifle shot. Cork captures Joaquin, Carlos Rodriguez's son. Rodriguez's men then execute Sanchez. Under interrogation, Joaquin reveals the cartel has been using Jocko's landing strip for drug shipments and that Ernesto Rivera, Rodriguez's son-in-law, has been consolidating power within the organization. Frank Harris leads Cork to the Jezebel Mine on Harris family land, where they discover a massive cocaine stockpile. Cork deduces that Jayne Harris is the mole within the Desert Angels: She overheard rendezvous coordinates at church and laundered cartel money alongside Brown.

Rivera orchestrates a hostage standoff at the Jezebel, arriving with the traitorous Deputy Crockett and holding Jayne, Jocko, and Michelle as hostages. He demands Joaquin's return but actually wants Joaquin dead so he can seize control of Las Calaveras. When Cork refuses to comply, Rivera shoots Jayne, then wounds Frank as Frank runs to his wife. Sheriff Chet Carlson kills Rivera with a sniper shot, and Crockett surrenders.

Cork, Rainy, Peter, and Mondragón decide to release Joaquin to his father, hoping to end the conflict. Mondragón threatens the Rodriguez family with total destruction if Peter is ever harmed, then departs with Joaquin for Mexico. In the epilogue, Peter returns briefly to Aurora, Minnesota, before leaving for Guatemala with Cork's daughter Annie to continue humanitarian work. A newspaper article reports the massacre of the entire Rodriguez family, attributed to cartel infighting but understood by Cork and Rainy as Mondragón's doing. On their first wedding anniversary, Cork gives Rainy a framed Pueblo prayer she taught him, which sustained him through his ordeal. They hang it above their bed.