A backup set of ropes catches the set piece, arresting its fall just in time. Since Cassidy is the poltergeist’s target, she decides that she needs to split up from her parents to keep them out of harm’s way. They’re walking to the next location when they pass a movie theater. Cassidy asks to take a break and see a movie while they’re at the Rue des Chantres. Her parents give their permission, on the condition that she doesn’t go anywhere else until they pick her up in two hours.

Cassidy and Jacob sneak out of the theater and enter the Veil, wanting to learn more about the poltergeist. Another ghost is there, however, and he tries to shoot Cassidy with a pistol. Jacob pulls her out of the Veil just before the shot goes off. Undeterred, Cassidy enters a different Veil. She and Jacob hide behind pillars, hoping that they’ll spot the poltergeist and be able to follow him, unnoticed. As they wait, being too long in the Veil makes Cassidy light-headed and short of breath. Eventually, she passes out.

When Cassidy regains consciousness, she’s back in the real world. Jacob begins to chide her for taking such a risk when a truck veers around a corner. The back door opens, and the contents begin spilling out. A giant mirror hurtles toward Cassidy, but Jacob pushes her out of its way. When it breaks, Jacob accidentally looks at the mirror’s fragments and begins to ripple and fade, like ghosts in the Veil do when Cassidy reaps them. Somehow, he frees himself from the mirror’s grasp and then disappears into the Veil. Cassidy goes in after him.

The poltergeist is there, but as soon as he knows that he has their attention, he runs away, like he’s playing a game. As Cassidy chases him, the Veil reforms, and she finds herself following the poltergeist into the Catacombs. She loses him when he slips through a small opening in a locked gate, but she comes away with a clue about his identity: the possibility that the Catacombs are where he died. Cassidy and Jacob exit the Veil with very little time left before her parents are due to pick her up at the movie theater.

Cassidy makes it back to the theater in time, though just barely, and her parents don’t suspect anything amiss. When they return to their hotel, the lobby is full of guests in wet clothes, and the Blakes learn that something in their room set off the fire alarms and sprinklers on the third floor. The irritated hotel clerk suspects their cat. Cassidy feels sure that it was the poltergeist. She sketches him and texts the sketch to Lara, who says that his clothes appear to be from the early 20th century. Cassidy remembers her father saying that people had gotten lost in the Catacombs and never made it out. She asks him if he knows who they were. Luckily, he has information about them in his research notebook. One of them, Mr. Blake reveals, was a seven-year-old boy named Thomas Alain Laurent, who disappeared in 1912 after sneaking into the tombs with his brother.

That night, Lara passes along a helpful tip from her uncle. She says that Cassidy can use sage and salt to ward off strong spirits. She had a package of them delivered to Cassidy’s hotel room, with the help of connections in Paris who belong to La Société du Chat Noir, or The Society of the Black Cat. Cassidy hides pouches of sage and salt in her father’s jacket pocket and her mother’s purse. 

Unable to fall asleep, Cassidy thinks about Jacob. She worries that he was able to pull free of his reflection in the mirror shards because he’s starting to forget his death, like a poltergeist. She eventually does fall asleep, but a series of car alarms wakes her up. She can hear Thomas’s voice counting in French. Looking out the window through her camera lens, Cassidy can see Thomas standing in the street. He gestures to her as if he’s inviting her to play. When she shakes her head no, his smile turns into an angry sneer, and then he’s gone.

Cassidy has a nightmare about Jacob creating a storm of paranormal energy and chaos again. This time, his eyes are red, and just before she wakes up, he looks at her and says, “stop me.” 

The next morning, Cassidy sees that she has several missed calls and texts from Lara, who has a new lead on Thomas. She discovered that his older brother, Richard, died 30 years ago, but Richard’s granddaughter, Sylvaine Laurent, still lives in Paris. Cassidy tells her parents that she’s interested in Thomas’s story and wants to interview Sylvaine. Pauline offers to take her while the Blakes are filming. On the train, Cassidy hints that Pauline made the offer because she didn’t want to accompany Mr. and Mrs. Blake to their next site, the Butcher of Marmousets, out of fear of ghosts. Pauline reasserts that she doesn’t believe in ghosts. Then, Cassidy feels a cold wind as the Metro screeches to a halt and goes dark.