Hess uses unorthodox methods to prove a theory about the Hartung case. The detectives chase a lead linked to a text message. Rosa faces another threat.

When a disturbing discovery provides a lead to a possible target, Thulin and Hess hatch a risky plan to lure the killer.

The detectives find inconsistencies as they dig deeper into the Kristine Hartung investigation, while the threats against Rosa take a terrifying turn.

Neither Thulin nor Hess can stop thinking about the unanswered questions hanging over their case. Rosa's career unravels as a childhood memory surfaces.

As the pieces of the Chestnut Man mystery fall into place and the perpetrator's motives become clear, Thulin and Hess fight to save innocent lives.