After waking up surrounded by dead bodies and no memory, Myfanwy Thomas is thrown into the world of the Checquy, a paranormal secret service where she's a high-level operative known as a "Rook" - and no one can be trusted.

While Myfanwy revisits the crime in search of her past, Monica discovers a dark truth about one of the victims - her lover and fellow agent. One of Myfanwy's dead attackers disappears from the morgue.

Myfanwy discovers a disturbing clue to her past, Farrier searches for a scapegoat for the bankside murders, and Monica goes undercover to attend an EVA auction.

While Myfanwy uncovers a twisted relationship with her psychiatrist, Monica and Gestalt scour London for a missing EVA who escaped after auction. Farrier makes a connnection wih a mysterious prisoner.

While Myfanwy returns to her childhood home, Farrier faces consequences at the Checquy and Monica copes with the discovery that she was betrayed by Marcus.

After a terrifying prophecy, Myfanwy's desperation leads her to a place to trust in a powerful enemy. But when her plans go awry, she is forced to run for her life while her memory slips away.

Myfanwy and Farrier quickly discover how dangerous life is outside of the Checquy, while Grantchester runs out of options. Myfanwy chooses between her freedom and Farrie's life.