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The killer moves through the crowded Grand Ballroom with a concealed knife. He is aware the FBI is watching Michael. As he counts down, the power cuts out as planned. In the chaos, he bypasses his decoy and moves toward his true target, Aaron Shaw. Approaching him from behind, the killer slices Aaron’s throat and melts back into the panicked crowd.

The video feeds from the ballroom go black. On the phone, Agent Sterling confirms to Cassie that Michael is safe. Cassie urgently informs Sterling that the killer is Beau Donovan and his real target is Aaron Shaw. Just then, the lights come back on, and a scream erupts over the line. The feeds show a horrified crowd around Aaron’s body. At the safe house, a devastated Sloane laments that her father didn’t listen to her warnings. Cassie reiterates to Sterling that she is certain Beau is the killer.

In the ballroom, FBI agents take a calm Beau Donovan into custody. They do not find the murder weapon on him. Back at the safe house, Sloane panics about the short legal window the agents have to charge Beau before he is released. Lia and Dean comfort her. Michael returns unharmed and embraces Sloane. United by the tragedy, the group resolves to find the evidence to prove Beau’s guilt.

Hours after Beau’s arrest, a grieving Sloane hacks the casino’s security system. Judd arrives at the safe house and offers assistance. While Michael and Dean analyze surveillance footage of Beau, they profile his anticipatory posture and elation after the murder. Judd theorizes the killer wrapped the weapon in something disposable, like plastic. Cassie and Dean deduce Beau planted the plastic-wrapped evidence on an unsuspecting guest.

Using security footage, Sloane maps Beau’s path through the crowd after the murder. Lia identifies three people Beau passed closely enough to have used as marks for planting his knife. Cassie and Michael recognize one as Thomas Wesley’s personal assistant. The team briefs Agents Briggs and Sterling, who leave to pursue the lead. Briggs informs them that Tory Howard believes Beau is innocent; she is refusing to cooperate. Cassie suggests Sloane is the only person who might convince Tory to talk.

Sloane calls Tory, and the two connect over their shared grief for Aaron. Sloane puts the phone on speaker, allowing Cassie and Dean to lay out the killer’s psychological profile. When their description of a resentful, manipulative, and performative individual matches Beau, Tory falls silent. Asked if she ever saw Beau draw a spiral, Tory breaks down, confirming he drew them constantly as a child. She reveals his traumatic past: Found abandoned in the desert at age six, he had selective mutism for two years.

In a holding cell, Beau Donovan is confident the FBI lacks the proof to charge him. Despite the risks of the footage and Tory’s testimony, he believes he will be released. His mission is not over: He must kill four more people to complete the ritual, claim a total of nine victims, and take his rightful place and “go home” (339).

The team watches a live feed of Beau’s interrogation. To rattle him, the agents show him crime scene photos from past kills by Nightshade. Agitated that the FBI has connected him to the secretive cult, Beau dismisses his lawyer. When Sterling taunts him as a failure, Beau rips open his shirt, revealing a symbol of a cross within seven circles carved on his chest. Cassie is stunned, recognizing it as the symbol from her mother’s coffin. Beau then begins convulsing from poison, choking out a few cryptic words about the cult before dying.

Cassie connects the symbol on Beau’s chest to her mother’s murder. She re-examines an evidence photo and realizes the white flower at the crime scene was origami. A memory surfaces of seeing a man—whom she now identifies as Nightshade—in Las Vegas a few days ago with a woman and a little girl. From Beau’s dying words, Dean and Cassie piece together the cult’s structure: seven leaders called the Seven Masters, a female prophetess known as the Pythia, and an heir the Pythia gives birth to, titled Nine.

Using Cassie’s description, police create a composite sketch of Nightshade, and a city-wide manhunt begins. As Cassie, upset by her encounter with Nightshade, imagines her mother’s abduction and murder, Dean comforts her; they kiss until Lia interrupts to let Cassie know that it is now her turn to be emotionally fragile. Michael comes in with news: The FBI has captured Nightshade. The team’s relief is short-lived, as Michael adds that during his capture, Nightshade injected Agent Briggs with a fast-acting poison.

Judd informs the team that Nightshade claims to have the antidote but will only speak with Cassie. At the interrogation facility, Cassie confronts him. Nightshade identifies the poison—it is rare snake venom that must be treated with antivenom, which the team can find at a zoo. He also confirms that the cult abandons unworthy children like Beau. He states the cult does not kill its Pythias, but adds that each new Pythia must kill her predecessor to assume the role. Before she leaves, he suggests Cassie herself may one day face this choice and gives her a hotel room number: 2117.

After Briggs receives antivenom, Cassie and an FBI team raid room 2117 at the Dark Angel Hotel Casino. Inside, they find a murdered woman and a small, silent girl named Laurel—the two people Cassie saw with Nightshade earlier. Laurel reveals the dead woman was a locally-hired nanny. She then shows Cassie a locket containing a recent photograph of Laurel with Cassie’s mother, Lorelai Hobbes. Laurel reveals that her other name is Nine. Cassie understands the truth: The body found is not her mother’s. Her mother is alive and is the cult’s current Pythia.

At a cemetery, Cassie, her father, and her team stand before a grave marked with Lorelai Hobbes’s name. They are burying the previous Pythia, killed by Cassie’s mother. They maintain this deception to protect Laurel, now in FBI custody, and to make the cult believe its secrets are safe. Cassie knows her mother is a captive who was forced to kill her predecessor. Looking at her found family, the Naturals, she vows to find the cult’s Masters and rescue her mother.