Plot

Gillian pays a price for her disloyalty to Diana, threatening the fragile equilibrium among creatures.

Miriam and Marcus greet Matthew at his estate and assure him nothing is missing from the lab, but Miriam takes a firm stance that he is at fault for drawing hostile attention to their research. Matthew investigates the lab and recognizes the scent of the intruder. After he leaves, Miriam insists they call Baldwin and tell him Matthew's judgment is severely compromised because of Diana.

Matthew tracks down Gillian and feeds on her, reading her memories of what she saw in the lab. He also takes her phone, which contains photo evidence, and leaves her in the street. Gillian manages to reach Sylvia's doorstep before passing out. Sigismund, the third witch on the Congregation, relays this information to Knox and Satu. They have differing opinions on whether Gillian was right to trespass on vampire territory, but they are all equally concerned that Matthew is studying witch DNA.

Back at Sept-Tours, Ysabeau takes Diana hunting to show her what vampires must do to survive, trying to discourage her from pursuing Matthew. Diana remains strong. She calls Sarah and Emily to ask about the Covenant, and she confesses her love for Matthew. Next, Ysabeau takes Diana into the adjacent town and shows her the church Matthew built during his human life. Inside are the graves of Bianca and Lucas, Matthew's wife and young son who died from a fever. Ysabeau found Matthew fatally injured at the base of the church tower, possibly after a suicide attempt, and sired him in the church. Ysabeau does not think Matthew will ever mate, because he can never have another child. Diana insists she will never leave Matthew regardless.

Matthew visits Hamish, who sees that he is deeply conflicted in his feelings toward Diana. He realizes his friend is more worried that Diana will discover his darkest secrets than he is about the Congregation. Hamish tells him love can't be controlled and he should let nothing stand in his way.

At the next Congregation meeting, everyone argues about who has the right to retrieve Diana from Sept-Tours. Baldwin insists that it is his responsibility alone. Satu asks Knox if he would consider siding with the other vampires against Baldwin, in order to capture Diana for further study. What she has in mind, an opening spell, is dangerous dark magic and Knox warns her against it. He also tells her in the strongest terms that she must avoid Gerbert, who is rumored to have kept a witch in thrall for centuries.

Nathaniel has kept up his daemon outreach and is meeting with a group at a local pub. Sophie comes in late and tells Nathaniel she heard her father's voice in a dream, repeating that she must tell the truth. She has a secret she wants to share with Agatha, and while Nathaniel is wary, he ultimately supports her decision.

Diana is sitting at Matthew's desk and discovers a hidden latch, triggering the opening of a drawer that contains seals and badges belonging to the Knights of Lazarus. Matthew calls her from Oxford and they have a strained conversation. Thinking of Diana compels Matthew to re-examine her DNA results and he makes a surprising discovery in the lab. Miriam finds him there the next morning and is equally excited by the data.

Marthe wakes Diana to tell her Matthew is on the way, and she runs to meet him. Matthew declares his love for her and performs the vampire equivalent of a marriage vow. He expects Ysabeau to send them away, but she accepts Diana as her daughter and vows to take up their fight. She praises Diana's courage, but privately she confides in Marthe that Diana's lack of magical control puts them all at risk.

Gerbert consults his captive witch again. She elaborates on the prophecy she gave earlier: Beware the witch with the blood of the lion and the wolf, for with it she will destroy the children of the night. Gerbert demands more information. She will only reveal that there are two candidates to fulfill the prophecy, one light and one dark, and one is close. At that very moment, Satu arrives at Gerbert's home. Domenico later finds Juliette at a club and baits her with news of Matthew and Diana, encouraging her to go to Sept-Tours.

Matthew shares the DNA results with Diana, revealing that she expresses every genetic marker they have discovered in witches. If such a powerful witch can still be born, perhaps creatures are not doomed to extinction after all. He starts to tell her about Gillian, but she has other things on her mind. Matthew carries her to his bedroom. He is reluctant for her to see his many scars; she wants to hunt down everyone who hurt him. They engage in the practice of "bundling", an old European wedding tradition that is apparently more intimate in France. Diana wakes before Matthew the next morning and goes for a run, but she is suddenly grabbed from the air by an unseen person.