The final season of A Discovery of Witches begins as the second season had ended: Matthew and Diana have returned to the present to find that Peter Knox has wreaked havoc on their family and friends, claiming the life of Diana’s beloved mother-like figure, Em. Diana is just able to see her final moments before she passes on, and it hits Diana like a punch to the gut.
Later on, having changed out of the clothes she had been wearing in the past, Matthew comforts her as she cries in her room. Diana is heartbroken that Em won’t be able to meet their child, but as she cries in Matthew’s arms, he tells her that he actually hears two heartbeats. She’ll be having twins.
The next day, others arrive at Sept-Tour, including Gallowglass, who hasn’t seen Diana in centuries, whereas it has only been a few days for her. They all sit at the grand table with Matthew at its head. He talks to his family and friends about the events that took place there, and that Peter Knox has brought his death upon himself, therefore vengeance will be carried out. However, Diana thinks that killing him would just make him a martyr—instead, they need to make sure everyone knows what he’s done and that he’s exposed for his unforgivable sins. It is during this conversation that Matthew first finds out about the vampire with blood rage who has been terrorizing Oxford.
We then find Matthew in his office mulling about. Phoebe comes in and introduces herself to him, but he is not in the kindest of moods and largely disregards her, as he thinks Marcus failed his responsibilities. Marcus, who has entered the office, calls Matthew out on his hypocrisy, because he had lied to him about him having blood rage. Matthew makes sure to point out that he does not have blood rage, but just carries the disease. This does not satisfy Marcus, so he and Phoebe leave Matthew alone again.
At the temple, Sarah Bishop is inspecting the site where her wife was killed when suddenly, the missing page Em had protected appears before her. Back in the castle, Diana comes to see her and asks why Em had been at the temple. Sarah tells her that she had been having visions and needed Rebecca. She used higher magic to talk to her, which pains Sarah, because she wants to know why she used a magic she had said shouldn’t be used. She then looks up at Diana and says that they could, in fact, ask her, but Diana says that she cannot use her power to change things in the past. She then reveals to Sarah that she’s having twins. Sarah, looking slightly frightened, asks her what they are. Diana replies that she doesn’t know, but she’ll love them no matter what. Through tears, Sarah then questions, “How will you keep them safe?”
Meanwhile, in Venice, the Congregation gathers for a meeting. They merge their keys to enter the meeting room, and Agatha of the Daemons is given the floor. But, of course, she is interrupted right away by one of the men to talk about the Oxford killings. Domenico says that the vampire doing the killings isn’t one he’s met before. Peter Knox then takes his chance to announce that Sept-Tour is holding vampires, witches, daemons, and humans alike in refuge. Agatha, however, finally gets a word in, and tells the Congregation that Peter killed one of his own, Emily Mather. Peter firmly denies it, citing the higher magic she performed caused her death.
Agatha continues to press, and asks about Marcus Whitmore’s injuries and what Peter was doing at Sept-Tour. Yet, he continues to protest that he did anything wrong. Agatha then, with such fervor, states to her peers, “I move that Peter Knox be removed from the Congregation for his crimes.” They vote—three against, and five in favor. Peter stands in anger, but gets told to relinquish his key and items and leave the island. With fire in his eyes, he glares at Agatha and tells her that this won’t keep her family or everyone at Sept-Tour safe—a clear threat. Immediately after the meeting ends, Agatha calls her son Nathaniel, and tells him to leave Sept-Tour and never call her again, otherwise Peter Knox will use her to get to him and his family.
Back at Sept-Tour, they hold a funeral service at the temple for Em. Diana and Sarah walk over, and Diana lays flowers on Em’s casket, and lights the candles with her magic. She performs the eulogy, allowing Em’s soul to move on as they “send you on your next journey.” Everyone then heads back to the castle, leaving Diana and Sarah behind. Sarah apologizes for what she had said to Diana earlier about the twins, and then pulls out the missing page. Diana takes it in her hands and tells Sarah that she’ll make Peter Knox pay for everything.
A new visitor arrives to their place of refuge—one who threatens it. Baldwin, Matthew’s brother and leader of the Congregation, asks his brother where he’s been. Matthew replies, nonchalantly, “London, just a few centuries away.” Matthew tells his brother that Philippe was at his and Diana’s wedding, but Baldwin doesn’t believe him. But, Matthew tells him how his heart changed and that he gave a blood vow has his wedding present to Diana. Baldwin is upset at this departure from conformity that he was used to seeing from his father, and that he withholds himself. He orders that Matthew and every other de Clermont stand down and not go after Peter Knox. Instead, he wants the vampire killer found, as that is more important. He adds on that although Philippe gave Diana the blood vow, both she and Matthew still answer to him, and he will determine if she’s actually a de Clermont. He says there’ll be a dinner that evening, “family only—but do bring the witch.”
At dinner, the only ones present at the grand table are de Clermonts and Diana. Everyone else, meanwhile, is eating downstairs in the kitchen, and celebrating Emily. At the upstairs family dinner, Baldwin states how he believes the Congregation keeps them safe. Diana disagrees, and that there is also no need for the Covenant anymore because of how times have changed since its creation. Baldwin slams the table in anger, claiming that to say that is a disgrace. He then brings up how this isn’t the first time a vampire and a witch have had a child together. The last time this happened, the witches banished the mother and child, and they ended up dying in the dessert. He is purposefully making everyone else angry, and Matthew realizes that. He excuses himself and Diana, but before they are able to leave, Baldwin orders that everyone who isn’t a de Clermont must leave by morning
Matthew and Diana take a walk outside, and she asks her husband if Baldwin is a de Clermont. He responds that he isn’t, exactly. At the end of the First Crusade, Philippe dreamt of establishing a homeland for creatures, but they had to reveal themselves to humans to do so, and Benjamin was one of them. But then, he threatened to expose them all, and Matthew lost control. Diana then realizes that she may have met him in Bohemia, but he had called himself Fuchs and didn’t say he was his son. Matthew grimaces, saying that he is not his son. He had made him a vampire so he couldn’t expose them without exposing himself, and then he abandoned him—a new, blood-ranged vampire.
Elsewhere on the grounds, Marcus meets with Gallowglass, who brings up the idea of forming a scion—a branch of the original family, but autonomous, so they can chart their own path. They bring this idea to Matthew, Diana, and the rest of their family (sans Baldwin, of course), but to Marcus’ displeasure, Matthew doesn’t believe that’s a good idea.
The next morning, everyone, including the de Clermonts, leave Sept-Tour, not willing to stay there with someone like Baldwin. Arriving at a safe house in London hosted by Fernando, who had been Matthew’s brother Hugh’s mate, Matthew, Diana, Gallowglass, Sarah, and Miriam settle in. Matthew believes that if they can figure out the origins of blood rage and trace it back, they can figure out the cause of it, what activates it, and more about their imminent extinction. Matthew believes that it is all connected to the Book of Life and the decline of all the species. Miriam says they would need a lab, and Diana knows exactly who can help them.
They go to Kensington and we reunite with Chris, who Diana hasn’t seen since before everything happened. She quickly catches him up on everything, and they then head to the lab. Chris asks for a bit more detail before he takes this project on, so Matthew shows him the blood cells of those carrying blood rage. Diana tells him everything about vampires, witches, and all the other creatures, but he isn’t sure to believe it without evidence—after all, he is a man of science. Diana shows him her magic by making a flower out of water from the faucet, and that immediately makes him believe in everything they said, and offers his help. Matthew tells him that species are declining, so they need to figure out why, and they also need to find a cure for blood rage.
Meanwhile, at the safe house, Fernando brings coffee over to Sarah, who’s upset that no one is talking about Em. Fernando asks her if she knows who Hugh de Clermont was. She doesn’t, so he continues, and tells her that he was Philippe’s eldest son and the two of them had been mated for six centuries. When Hugh died, neither his loss or his grief were acknowledged by the family. It’s been seven hundred years since then, and Fernando has yet to have those things acknowledged. Sarah tells him that he deserves to have those feelings recognized. He then tells Sarah, “Grief never really goes away. It gets quieter, slower, and sometimes it comes rushing back like the sea.”
Back at Sept-Tour, Baldwin meets with Domenico, who says the killings all happened where Matthew and Diana had been. The killer has been following them, and even stole their portraits that had been painted while they were in the past. He gives Baldwin an envelope with photos of the killings and leaves him to look over them. We land on Baldwin’s ring—black, with stripes. Then, we go to an entirely new setting and see a mystery man with that exact same ring. This mystery man gets a call and is told that “they” got back, so he responds that he’s heading to them now. He leaves, and we see that on his computer is a photo of Diana. He walks out of the hotel room, leaving some bloody, very dead people inside. Is this the vampire with the blood rage?? And what does he want with Diana??? We shall see next episode, but it’s safe to say that the final season of this fantastical, magical show is off to an exciting start.