The investigation has fallen off track, and Thomas is back in Germany. Helene has bigger things to worry about. A criminal she put behind bars has been released and is out for blood — Helene's blood.

The positive identification of the murder weapon leads Thomas down a rabbit hole of World War II memorabilia collectors. While Thomas's pursuit turns up solid leads in the case, it also leads him straight into danger.

The detectives' leads are drying up. The pair moves their investigation from land to the depths of the sea to investigate a shipwreck from 60 years ago.

As the investigation grows, so does the body count. Just as Thomas makes a break in the case, an explosive argument between him and Helene threatens to jeopardize the entire investigation.

Personal and professional boundaries are blurred between the detectives. Meanwhile, the pair pieces together all of the clues to make a shocking discovery about the killer and his motives.

Detectives Helene and Thomas are quickly thrust into their undercover roles as a married couple. The pair get acquainted with the town's most prominent personalities and begin to stitch together clues.

Helene and Thomas's cover is put to the test during a double date with a prominent local couple. As new leads come in, the detectives take unexpected risks and break laws in the pursuit of clues.

In a town where distrust for the police runs rampant, two detectives go undercover as a married couple to try and solve the year-old case involving the murder of a German surfer.