Grace find notes asking for help folded into tiny origami shapes outside a high-rise city apartment building, and then a physics textbook with tiny writing between the lines is dropped from a high window. Grace has secrets that make her interactions with the police difficult, and she asks her workmate Linda to assist. When Grace abruptly resigns from her job and disappears Linda asks Hunter Grant, ex-army and with a pragmatic view of justice for help, and he reluctantly agrees to help find out what happened to Grace. Within a short space of time a high-powered lawyer arrives from the US, and shortly after his meeting with Hunter, a "cease and desist" letter arrives from the Cayman Islands. Inspector Bakker - a woman, who in Hunter's words "looks as if she would be useful in a brawl, provided she was on your side" - takes instant exception to his involvement and threatens to arrest him for interfering in an investigation. Hunter's partner Dao sets out alone on a dangerous mission, driven by a compulsive need to find out what has happened to the girl who wrote the notes, and Hunter looks death in the face when he decides to risk everything to put an end to the Darknet forces that threaten their lives.