Some doors should never be opened. Former detective Mara Engel thought she had left the darkness behind. But when a series of cryptic murders begins—each tied to a mysterious symbol and an old case she tried to forget—she is pulled back into a world where nothing is as it seems. As the body count rises and the clues grow colder, Mara realizes the killer isn’t just playing a game. He’s sending a message. One that’s personal. One that only she can understand. A twist-filled psychological thriller where trust is a weapon, the past is a puzzle, and the truth might be the most dangerous key of all. This is the English edition of the German thriller “Der siebte Schlüssel,” written under the pseudonym Matteo Grimm.