Animal lovers, please be aware that there are distressing scenes in tonight's episode.
Van der Valk's final case of the season begins in an ancient castle outside of the city, where a magic ritual takes place. Psychiatrist Nik Delacorte (Joris Smit) and brain surgeon Isaak Engelhart (Steven Pacey) set spells to summon a demon. Downstairs, their followers link hands in a protective circle and wait. But Isaak’s granddaughter Katya Alsteen (Olivia D’Lima) becomes concerned at the cries for help coming from upstairs. Hans Lansing (Poal Cairo) the leader of the group, reminds her that the door must be locked until daylight, otherwise terrible things will happen. Another participant, Valentijn Meijer (James Atherton), is concerned enough that he goes outside to his car and calls the police.
That’s how the team becomes involved with the supernatural, giving Van der Valk the opportunity to utter cryptic comments about evil amongst us and practice magic coin tricks. Van der Valk and Lucienne open the locked door to find Nik dead, stabbed, his eyes gouged out, and Isaak completely out of his mind. The rest of the team finds disturbing evidence, as you’d expect. Hendrik cheerfully announces Isaak, who’s been taken away for medical care, couldn’t have been responsible for the eye-gouging because it’s a messy business and his hands were clean. In case things weren’t weird enough, there are cloven-hoof footprints in the heaps of sand that hold candles in place on the floor.
Katya is angry and upset that she’d agreed to accompany her grandfather to the ritual. He wasn’t even an official member of the group, the Order of the Blood Moon. Valentijn assures Lucienne it’s mostly harmless fun, although the true believers mutter about breaking protective circles. Van der Valk isn’t having any of it, and the first job assigned to Eddie back at the office is to find plans of the castle, suspecting there is another way into the murder scene.
As he and Lucienne leave, she shows him her new motorbike — is this another indication of a mid-life crisis following her infidelity in the previous case? He mentions that he’s going to meet with Lena, and Lucienne seems pleased that a reconciliation, or so she thinks, is on the way. She interviews Nik’s widow Isabelle, who suspected an affair, not a ritual, would end their marriage. Isabelle has a bandaged cut on one hand that she attributes to clearing up after her children broke a glass bowl. Van der Valk, however, thinks she may have cut herself in the process of vandalizing Nik’s office. He finds protective rosemary and salt in the entranceway, dangly magic things, and graffiti.
Van der Valk meets up with Lena, and it’s awkward from the get-go. She bought a coffee for herself, but not for him. (She didn’t think they were at "the buying coffee for each other" stage.) He seems to have recovered from her sudden appearance in front of his colleagues, and it got him thinking about seeing her, but he’s made his decision. They can’t go back, and he won’t, as Lena suggests, go forward. He kisses her on the cheek and she offers to drop off the key to his boat.
In happier news, Hendrik is having a splendid time examining Nik’s body. Nik was stuffed full of stimulants and hallucinogenics, and even better, he had an elaborate tattoo on his back, a series of Latin palindromes arranged in a square. Isaac’s fingerprints are on the murder weapon. Citra has added a few pictures of demons to the incident board and has analyzed the membership of the Order of the Blood Moon, discovering that the current roster includes three judges, two politicians, and one rock star. Seven members left the group in the past year and she’ll find out who they are.
Citra and Eddie are sent to Hans’ Tattoo Shop to find out more about the design on Nik’s back. Eddie lingers outside before admitting to Citra that tattoos upset him, not because he had a bad tattoo but because he had a bad experience with a tattooist who kidnapped his daughter. Eddie had been ordered to shoot him if necessary. Eddie hit the tattooist, but unfortunately, the bullet also caught his daughter. Although both survived, it is still a topic that upsets him. Hans says Nik’s tattoo was protection against demons because they can’t read palindromes. (We all knew that, right?) However, when Hans hears about the attack, he tells them the tattoo suggests a war between two practitioners of magic.
Van der Valk and Lucienne visit the hospital where Isaak is being treated, and while they attempt to talk to him and his granddaughter, he prowls around, trying to establish a protective circle. In between incoherent ramblings, he reports that a glass of wine vibrated, and Nic become vulnerable when he left the protection of the magic circle they’d created. There was someone else in the room, Hecate’s agent on earth. Katja tells them he’s referring to Angelique Rousa (Eleanor Fanyinka), another practitioner of magic, a very modern witch with a huge social media following. She has an alibi for the time of the murder given by her assistant/lover.
She tells the detectives that she knew both Isaac and Nik, but their magic practice disappointed her in its old-school style. She worships Hecate, a much-maligned, potent goddess. Now both men are dead to her — just as Lucienne’s siblings are dead to her. Seeing Lucienne’s alarm, Van der Valk moves to protect her, but Angelique continues with a traumatic story from Lucienne’s childhood. As they leave, Lucienne tries unsuccessfully to laugh it off and refuses to speak to Van der Valk about it.
The team meets up in Cliff’s bar to compare notes. Citra has researched all seven of the people who left the Order, and everyone except a young woman, Mila Manderfeld, has been accounted for. Mila worked for Hans, who runs a nightclub in addition to his tattoo shop, and was a patient of both Isaak and Nik. Meanwhile, Hans intercepts Angelique as she leaves her studio to ask if she did something to damage the summoning. She laughs at him and suggests that he has more reason than her to disrupt the group. With Nik dead and Isaak incapacitated, he is now poised to take over as leader.
Eddie found an older map of the castle showing a hidden entrance to the room where the summoning took place. He and Van der Valk find a doorway in a room converted to a bar with practicals and props for the summoning special effects (the vibrating wine, demonic hoof prints, etc.) and stone steps to a hidden panel door. Henrik and Citra leave for Hans’s bar, where party animal Henrik turns out to be a well-loved regular. Hans, Valentijn, and Katya are also there; Valentijn joined the Circle after Mila left, but Hans and Katya remember her and agree that she was out of place, leaving of her own volition. They claim not to have known she was in a relationship with Nik.
Isaak, meanwhile, plans a break out from the hospital after dabbling around with some blood on the wall, replicating the palindrome words. He attacks a nurse and escapes just as Lucienne rides there to visit him, arriving too late.