When Matthias Trockland, who turned witness for ZERV, is found dead, ZERV West Commissioner Peter Simon and Karo Schubert from the Berlin homicide squad work together to solve the mystery surrounding Trockland's death.

When ZERV officers find a large cache of banned weapons in the decommissioned NVA military site, Simon and Karo presume that Trockland may have been killed because he was pursuing the illegal NVA arms trade.

Reiko Böttcher is arrested as a suspect in the arms theft and the explosion at the NVA site. Reiko makes a startling confession, which helps Simon and Karo get a step closer to the truth, but he also ends up risking his life in the process.

Böttcher's death confirms that Simon and Karo are on the right path. At his funeral, they identify a person of interest known as `KoKo-Wutzke', Gärster's former boss, and a man from Karo's complicated past.

Böttcher's death forces a distraught Gärster to turn himself in; in ZERV custody, Simon makes an unauthorised deal with Gärster without the knowledge of his boss; Karo makes a shocking discovery about her father.

Frauke Beckmann identifies the mole within the ZERV; Karo is in Wolfsburg meeting her father, who gives her an important lead into the case.