Contains spoilers for this episode and earlier episodes.
Rust and Marty force Geraci to watch the recording of Marie Fontenot's murder and press him about the abandoned investigation. Marty then notices an ordinary detail in an old photograph: a house had been painted green. He connects that paint with a child's description of green ears, and the partners trace the contractor through records to the Childress property. Before going there, they arrange for evidence and a call for help to reach other investigators.
The property brings them to Errol Childress and the tunnels he calls Carcosa. Rust follows him inside, while Marty searches for a telephone and tries to catch up. Errol wounds Rust; Marty arrives and is injured too before Rust shoots their attacker dead. Backup reaches the house and both detectives survive. The physical evidence connects Errol to Dora Lange and the later killing, while the discovery of many bodies exposes crimes extending far beyond the original scene.
Recovery gives the men time to face what their investigation did and did not achieve. Marty receives a visit from Maggie and their daughters. Rust wakes from his coma troubled that everyone responsible has not been caught, and the wider Tuttle connections do not produce complete accountability. Outside hospital, he tells Marty that he felt his lost family's love while near death. Their conversation turns toward light and darkness, and Rust allows himself a hope that his earlier view of life had refused.