The next morning, Neblett reassigns Peter to work with DCI Nightingale. They meet at a Japanese restaurant, where Nightingale confirms that ghosts are real and reveals he is the Metropolitan Police’s sole specialist in supernatural crime. Peter recounts Nicholas’s testimony, and Nightingale explains that supernatural events leave traces called vestigia.

At Westminster Mortuary, Nightingale instructs Peter to place his face near Skirmish’s severed neck. Peter senses the presence of a small, yappy dog, accompanied by violence and laughter. As they leave, they encounter DCI Alexander Seawoll, the Senior Investigating Officer on the case. Seawoll angrily warns Nightingale away from his investigation and questions why he is taking on an apprentice, referencing a prior arrangement based on the belief that magic was in decline and Nightingale would not need a successor. He privately advises Peter to distance himself from Nightingale.

Peter and Nightingale visit Skirmish’s flat in Dartmouth Park, where they find evidence of a dog. Peter contacts Leslie, who confirms no dog was mentioned in the Murder Team’s reports. They locate the dog, Toby, with Skirmish’s upstairs neighbor, who explains that Toby is hiding because he bit a man named Brandon Coopertown on Hampstead Heath before Christmas. They drive to the Coopertown residence in Hampstead, where they meet Brandon’s wife, August. She describes the dog attack and mentions that Brandon is currently in Los Angeles and due home that night. 

That evening, Peter tells Leslie that Nightingale is a wizard. They return to Covent Garden with Toby to track supernatural residue. Nicholas briefly appears, warning Peter that Nightingale is “touched” and suggesting Peter ask about his year of birth. Toby picks up a scent and races to a bus stop on the route toward Hampstead. Peter asks Leslie to check the bus CCTV footage.

The next morning, Leslie reports finding footage of Brandon Coopertown boarding a bus minutes after Skirmish’s murder. She and Peter drive to Hampstead and find Nightingale already staking out the Coopertown house. Toby suddenly begins barking furiously, a window shatters, and a woman screams. They discover the Coopertowns’ infant son has been thrown from a second-story window. Leslie attempts CPR while Peter calls an ambulance.

Peter and Nightingale rush inside to find August Coopertown badly beaten on the upstairs landing. A man they believe is Brandon Coopertown stands over her, his face grotesquely distorted, holding a long wooden baton. Coopertown strikes Nightingale with tremendous force when he tries to tackle him, flees downstairs, and collapses dead in the hallway. Nightingale orders Peter outside to preserve the crime scene.

Emergency services and police arrive at the Coopertown house. Nightingale takes command, and when DCI Seawoll arrives, he instructs Peter and Leslie to omit any supernatural elements from their official statements. They give carefully doctored testimony at Hampstead station. That night, Leslie seeks comfort in Peter’s room, and they fall asleep together platonically.

The following day, Nightingale takes Peter to the mortuary to meet Dr. Abdul Haqq Walid, a cryptopathologist who specializes in supernatural cases. Dr. Walid explains that Coopertown’s facial bones were pulverized and his skin overstretched, consistent with a magical disguise spell called dissimulo that collapsed and killed him. His brain shows severe degradation from the magical overuse required to maintain the spell.

At a nearby pub, Peter formally requests to become Nightingale’s apprentice. Nightingale warns him that there is no turning back, but Peter insists. The next day, they visit the commissioner at New Scotland Yard. Nightingale argues that he needs an apprentice as magical activity has been increasing since the 1960s. The commissioner agrees and administers an ancient oath, making Peter officially Nightingale’s apprentice.

Nightingale informs Peter that he must now live at his residence in Russell Square. Leslie helps Peter pack, and they plan an evening out. Peter arrives at a grand Georgian building called the Folly, bearing the inscription “Scientia Potestas Est” above its entrance. Nightingale explains that the Folly has been the home of English magic since 1775, when it was founded by Sir Isaac Newton. Peter meets Molly, an unsettling, sharp-toothed maid who serves the household.

That evening, Nightingale and Peter collect August Coopertown’s grieving parents from Heathrow and escort them to a hotel. Later, while Peter and Leslie queue for a cinema in Leicester Square, a woman in line suddenly attacks the ticket seller, attempting to strangle him. Peter and Leslie subdue and arrest her; she is eventually released on bail. Peter suspects a supernatural element but cannot confirm it.

The next morning, Peter’s first magic lesson takes place in a disused chemistry laboratory at the Folly. Nightingale demonstrates a spell called a werelight, creating a glowing sphere of light in his palm. He explains that Peter must sense the mental shape, or forma, of the spell to replicate it. Peter attempts it repeatedly but fails to produce light, though he begins to sense an echo of the forma in his mind. Nightingale assigns him hours of practice, explaining that mastering this first step is both essential and a test of his aptitude.