In the season premiere, Bash along with the rest of the people at court gather to hear the announcement that Mary, makes about the plague. Kenna finds him after the gathering to tell Bash that people are being isolated even if they are only seemingly unwell. He tells her that there isn't enough food for every household at court and that he's managed to keep some in their quarters. He tells her to find Pascal and secure themselves in their chambers. They kiss before parting ways. He later checks in on a guard named Nathan to ask if he's seen Kenna. The guard mentions he looks tired, Bash tells him he's been securing the lock down of the castle. Nathan tells him that he and Kenna should also be locked down. He says he did but Kenna left a note saying she went out to look for Pascal. When a young girl drops her doll, Bash picks it up. When he goes looking for Kenna he calls out her name and a voice inside an infected room says here. When he opens the door, a woman badly infected with plague falls in his arms. She starts running towards the gallery, he tries to tell her to stop but when she doesn't he stabs her. Guards come to help him but he tells them to stay away as he is surely infected as well. Later, Bash begins to hallucinate about the little girl who's doll he picked up. He asks her if she's dead and if he is, if he was infected, she replies that she is and he'll live. She tells him there will be a reckoning, before he wakes out of the hallucination or dream. He hears Kenna screaming his name, he rips the boards off the door and frees her from the room. He strolls in and hugs her spinning her around. She tells him about the death of Pascal, he then comforts her.
In Drawn and Quartered, Bash finds victims of the Plague in a locked room. He tells them to wrap the bodies with care. He says they have to give them proper burials so their souls can rest. When Francis returns to the French Court, he asks Bash to join the privy council. Bash learns that Narcisse used the plague as a way to murder families and seize land deeds in order to make himself a more powerful figure. While out near the community grave designed for plague victims and important documents, he encounters a citizen who confirms what the little girl in his hallucination told him - the door between the living and the dead is cracked and due to mistreatment and the way they died, some of the dead aren't wanting to go through. They don't have a guide to see them through to the other side, so they're lingering, just waiting for the opportunity to strike.
Back at the castle, Bash tells Francis that he thinks they need Nostradamus, whose supernatural gifts could come in handy should the reckoning that he's heard about come to fruition. He elaborates on what the death are seeking. At the end of the episode, Bash gets Francis to grant him the title of King's Deputy, a way for him to have a legitimate title for the first time and a way for him to work at court without being on the council.
In Coronation, Bash attends a celebration, to tell Francis of his findings concerning Lord Montgomery and Caroline. He then dances with his wife before a woman comes to him asking for help claiming that Lord Barnard killed her husband. Bash ushers her out of the room. When doing research for evidence of Lord Barnard murdering the woman's husband. He finds death records which prove that she was in fact telling the truth and that her husbands throat was slit.
He wakes up the next morning to a overjoyed Kenna with the fact that the Barnards have gifted them with a château. Bash quickly realizes and tells Kenna that this isn't a gift but indeed a bribe so he won't find Lord Barnard guilty of murder. He's content with the fact that he is closer to proving his guilt than he previously thought. Later that day, he attends more celebrations in the Tent City. When Charles Schuler arrives angry and threatening the French. When he says he will leave to look for his missing prisoners himself Sebastian tells him he won't do so with weapons because he is on French soil and orders the guards to take them away. He later returns to his chambers angry with Kenna because she had burned the proof of Bouchards murder. He's told that she didn't do it for the bribe but to save his life. He tells her that he will fight for what he believes no mater the risk. He along with everyone else at court attends Mary and Francis' Coronation.
In The Lamb and the Slaughter, accompanied by Louis, Sebastian goes to the village in order to interrogate a shepherd about what he knows of the mysterious riders who tormented him. He's told by the man that the riders offered him a mark that would protect him and his family in exchange for him renouncing his faith and god. Later that night during the banquet, he returns to court to tell Francis about what he and Louis learnt of the riders. Also he congratulates his brother on the news that he is to be a father twice over. The next day he and all those invited attend Jean-Philippe's Christening at church. Soon after, he and Louis once again return to the shepherds home only to find that it had been ransacked and the family had been murdered by the shepherd because he said no to the riders. He orders the guards to strip him, only to find the mark of the riders which they had forced upon the man.
In Blood for Blood, he goes to see Francis and Mary to tell them about the attack on a Protestant service. He and Leith are ordered to go help however they can, to find out what happened and capture the guilty party. On their way he tells Leith to find the victims and sure them they'll be protected while he finds the attackers. He returns to court with the men who attacked the Protestants. While he and Francis take a stroll outdoors, they discuss the manner of the Protestants and Catholics further. Even after Catherine's warnings, Francis orders Bash to arrest the attackers. The next day he attends Greer and Lord Castleroy's Wedding.
He informs Francis about Mary and Catherine's disappearances in Three Queens.
In The Prince of the Blood, Bash introduces Kenna to his younger half-sister, Claude whom has returned to the French Court. Soon after, Bash reports to Francis on Narcisse’s movements. He says Lola visited the man but he wants to know about the nanny. Bash asks him if he hired Montgomery to kill their father. Francis says no and says he killed their father himself by taking Montgomery’s place. Bash says he understands and knows what a danger their father was. Francis says Narcisse knows and has Montgomery hidden away as leverage. Francis says he needs a way out so he doesn't have to sign the edict. He tells Bash he can’t ever tell Mary. He tells Bash the Nanny knew a lot and may know where Montgomery is. Bash pledges his help and says they’ll find them then kill Narcisse. Later, Kenna has a gift for Claude and Bash tells her that Claude does not make female friends and tells her not to bother. They flirt and he tells her he has to leave for court business. He tells her he loves her and leaves.
The next day, Bash returns and tells Francis that the nanny is dead and has been for weeks. Francis says Mary keeps trying to buy him time. He says he can’t put her life at risk and tells Bash to ready a boat to get Mary out in case he’s accused of regicide. Francis says he has to face the consequences and better he than France. He tells Bash to make sure Mary is safe. Bash says it could cost him his life but he says he has to do it. Later, Kenna complains to Bash that Claude is ignoring her. She asks what the issue is and Bash says she’s jealous and petty because Kenna is the most beautiful woman at court. After he leaves, Claude sneaks up on him and asks why he hasn't said hello. She asks if he misses the way they used to play. He says nothing would have ever happened between them if she hadn't convinced him that Henry wasn't his father. He says it won’t happen again and walks off.