The word “fugue” has two meanings. In psychiatry, a fugue is an altered state of consciousness; the person loses memories and wanders away from home. In music, a fugue is a compositional technique with two or more voices built on a subject that repeats frequently during the composition. Both ideas are woven through this week’s episode.

In a room at the Sanctuary, Will, Declan, and Helen use stunners to try to subdue an Abnormal, but the stunners are not working. Helen tells Will and Declan to keep it in the room. She leaves and gets a bigger gun. The bigger stunner works. The Abnormal collapses and changes. The grey Abnormal disappears, revealing Abby.

Abby has been taken over, invaded, by an unknown Abnormal. Helen’s treatments are not working, including the DNA inhibitors. Will is frustrated and feels helpless. He understands what Abby is going through; he has lost his self twice. Helen reassures Will that they will find a way to help Abby.

Henry and Gavin, Abby’s FBI partner, investigate the source of Abby’s infection. Abby and Gavin were called to investigate a sighting of an unusual creature about two days ago. Since then Abby hasn’t been herself.

Will sits by Abby’s side in the lab. Declan comes in and tries to get Will to leave so he can get some sleep. Will refuses. Declan plays music. Abby wakes up and sings everything she says. She cannot understand speech.

Helen scans Abby’s brain and discovers part of Abby’s brain is overstimulated, making her only capable of understanding certain frequencies. Will refuses to sing. Helen sings, and Helen and Abby sing their conversation. Abby does not know what happened to her, and Helen tells Abby that she is trying everything to find a cure.

Henry and Gavin investigate again. Gavin calls Abnormals “monsters,” and Henry tells Gavin that “monsters” is a term they don’t use. Henry tells Gavin to scan the area; Henry is about to leave when Gavin finds something—a cocoon.

After conducting tests, Helen learns that Abby is infected by a new parasite. An Abnormal created a new parasite, put the parasite in a blood tick, and planted the cocoon for Abby to find. Helen realizes that she’s being tested. If she fails, then the Abnormal responsible for the parasite will infect the human population and turn humans into Abnormals. Helen has to find a cure so she can stop an invasion.

Will talks to a sedated Abby. His mother used to sing to him all the time when he was a child. After she died, he stopped singing. But he loves Abby, so, slowly at first, he begins to sing. “Just stay,” he sings repeatedly.

Will stops when he sees Gavin. Will accuses Gavin of being a lousy partner. Gavin should have kept his eyes on Abby. Gavin tries to apologize, but Will’s anger prevents him from accepting it.

Abby wakes up. Will sings, but he’s not singing to Abby. The creature has taken over Abby, but she has not transformed. The creature feels alive and wants to experience sensations. “Abby” wants to grab Will, and he tries to stay away from her, asking for Abby to come back. “Abby” finally pins Will on the bed, wanting a kiss. She is sedated by Helen and Declan.

Helen and Henry spend a lot of time doing research.

Will dozes off. When he wakes up, Abby is gone. Will finds Abby on the roof. They sing, and their lines overlap. Will confesses his love for Abby and asks her to “just stay.” Abby loves him too, but she feels as though she is fading away and losing herself. Abby is on the ledge, and she falls.

Will rushes towards her, but he can’t grab her. As Abby falls, the creature takes over, and she transforms into an Abnormal. After Abnormal-Abby lands safely, Helen stuns her.

Helen, after conducting more scans, realizes that Abby is not infected with a virus. Instead, she is being transformed into a new form of life. Helen tells Will that they need to prepare for the possibility that Abby might not recover. Will’s anger flares. “Figure it out!” he demands of Helen.

As Helen does more research, Helen imagines her father is beside her. Her father sings a song as she slowly realizes a possible solution. The scene is touching and gives us a reminder of how close Helen was to her father, of how much she has lost.

Helen shares her idea with Will. Her father had a theory that the most powerful invasive DNA wants to define and to express itself, transforming the host into something more, like how vampires transform humans. Helen proposes a solution: implant a simple creature into Abby; the aggressive DNA will take over the simpler creature without causing Abby any harm until the new creature reaches maturity. When the new creature is mature, it will want to leave Abby, and it will have to do so in a violent manner. Helen assures Will that she can remove the new creature before any harm comes to Abby. Helen admits this idea is risky, but they are out of options.

Will accuses Helen of being intoxicated with the idea of creating new life; although he doesn’t call her a Frankenstein, his tone implies it. He says that Helen will not grow a monster inside his girlfriend; he’s determined to stop Helen.

Helen has Declan and Henry put Will in a cell. Henry guards the cell. Will tries to convince Henry to let him out. Henry tells Will that he is letting emotions overrun his logic. Henry has faith in Helen and trusts her to save Abby. Henry is stunned by Gavin, and Gavin lets Will out of the cell.

Helen and Declan perform surgery on Abby. The implant is successful, and the simple organism attracts the aggressive Abnormal DNA. However, the new creature matures faster than Helen thought it would, and it bursts out of Abby’s side before Helen could surgically remove it. Declan catches the creature and puts it in a secure container.

Will arrives and sees Abby crash. Will turns and slides down the wall. He sings “just stay” repeatedly. Helen and Declan use the defibrillator and successfully bring Abby back.

Abby recovers at the Sanctuary. Will tells her that he thinks he’s cursed; when you get close to him, you get a target. Abby tells him that he won’t lose her and that her “possession” has brought them closer. They kiss.

Will stands by a window. Helen cautiously approaches. Will has been avoiding her all day because he needed space. He thanks Helen for saving Abby, but Helen notices that Will has something more to say. Will tells her that he thinks the procedure should have never happened; Helen steamrolled her way through any compromise and ignored his ideas. Helen tells him that Will is a good soldier, and that he could run the Sanctuary by himself. Helen admits to being used to getting her own way, but she admires how Will can fight for what he believes in, which is why she selected him to be her protégé and her successor. Helen is very proud of him, even after he doubted her plan.

Many TV shows have had a musical episode with varied results. Because singing is the only way to communicate with the “possessed” Abby, the musical numbers are clever and plausible. The overlapping lines mimic real conversations, and the music enhances the emotions of the scenes without overwhelming any of the moments. Two standout scenes are the rooftop scene between Will and Abby and the library scene with Helen and her father. The skilled cast created the right tone and resonance. If you’ve never seen the show before, you believe the love between Will and Abby by the way they look at each other, how Will pleads with Abby to stay, and the turmoil Abby has because she loves Will, but she would rather die than lose her sense of self and put others in danger. The moment with Helen and her father had the right mix of sentimentality and tenderness. Having her father sing to her as she finally figures out how to cure Abby gives what could have been a routine “Eureka!” scene depth and significance.

The musical fugue is evident in Will’s repeated refrain of “Just Stay” and how many of the musical numbers were conversations between two people. At first I thought the psychological fugue only described Abby, but it also describes Will. Abby does lose her way for a while, and Helen and Will are able to bring her back—Helen with science and Will with love. Will slips into a fugue state when he doubts Helen’s plan. He forgets to have faith in Helen and drifts away from home by trying to stop her. Helen brings him home by telling him that she sees him as a worthy successor. Will had to learn that sometimes you have to make risky decisions that place the ones you love in danger even as you try to save them. Helen has had over 100 years to learn this lesson, so she understands Will’s actions.

‘Fugue’ is another strong episode. On the surface the episode seems simple, find a cure for Abby, but the structure, the writing, the music, and the performances create an intimate exploration of love, the love between friends and the confession of romantic love, and of faith, the faith you place in others and how you have to trust that faith in dire times.

A special episode of ‘Sanctuary’ will air on Tuesday, November 29.

If you missed the previously aired episode, be sure to read our ‘Sanctuary: Icebreaker ‘ recap to catch up.