Harry is at his apartment taking his once-a-year stab at exercising when Murphy comes in and demands to know what he's been doing. She's received a report of a green explosion in the vicinity and figures that Harry is involved. He insists that he isn't but agrees to go with her so that she can pay him to consult. Talk turns to the necklace that she always wears and Murphy explains that her nine-year-old daughter Anna gave it to her.
As Harry goes to get changed, Morgan barges into the shop, sword drawn, and tells Harry to activate his defenses. Murphy draws on the Warden and Harry tries to defuse the situation. Before he can, three more Wardens--Wallace, Soto, and Amber--come in, carrying a wounded Ancient Mai. Bob comes out, sees what's going on, and quickly steps back through the wall before Murphy can see him. The lights flicker and a cloud of impenetrable blackness closes around the apartment.
Amber reactivates the lights with a touch of magic, while Mai tells Harry not to tell Murphy anything. As he demands answers, a ghostly figure in white appears in the darkness. Soto notices it, goes to the door, and reaches out to it, saying the name "Lydia." Before Morgan can pull Soto back, something in the darkness sucks Soto's out of the apartment, tearing apart his body in the process.
As they close the door, Murphy demands answers and Harry explains that the dark force is from the Other Side. Amber finally speaks up and says that it's death. Harry asks Morgan who Lydia was to Soto, and the Warden explains that Lydia was his sister, a Warden who died in the line of duty. They explain to Murphy that Soto saw a spirit from the Other Side but she says that she can't deal with it. Morgan tells Harry that he needs somewhere safe to keep Mai and Harry directs them to his bedroom. He then has Murphy sit down, picks up his hockey stick, and demonstrates some magic for her, revealing the invisible protection runes scattered throughout his apartment.
Morgan comes back downstairs and Harry asks what they were messing with. The Warden refuses to divulge more secrets in front of Murphy and admits that they only came to Harry because he was close. He asks if Harry is going to help and Harry reluctantly agrees. As they go to Harry's lab, Morgan starts to talk about wiping Murphy's memories. Harry, furious, slams him against the walls and says that they're not going to tamper with his friend's mind. Once Harry gets hold of himself, Morgan suggests that the building is covered in a layer of spiritual material like paint, and Harry suggests that they thin it. The Warden agrees, suggesting that they create a coherent burst of light.
Harry draws out a ritual circle while Morgan stares pensively off into space. He finally admits that he trained Soto and blames himself for Soto's death. Harry tells him to focus and they combine their magics, through staff and sword, to generate a beam of light into the darkness. It fails to penetrate and the backlash sends them flying.
Murphy runs to investigate and Bob comes out, much to Murphy's surprise. The spirit asks to talk to Harry in private. Once they're alone, Bob warns Harry that it was cast from the inside. Harry already knows, having checked the defensive sigils earlier. They wonder who did it and Bob warns that the material is everywhere, even beneath the floor. Harry asks Bob to lie low and watch for anything suspicious.
As Bob agrees, Morgan calls Harry out and warns him that the darkness is moving. It seeps in through the door and the two men retreat as it covers the storefront. When Amber comes down, she tells Morgan that they should tell Harry the truth so that he can help them. Murphy agrees, demanding answers. Morgan explains that they were going to a meeting at Ecker Park. There was an explosion from above and green fire. Before Morgan can tell them the likely source of the attack, Mai comes out and tells him to stay silent. When Harry objects, Mai says that he's just like his mother and refuses, and Wallace gets her back to bed
Morgan and Amber try to work out a spell to penetrate the darkness. Once Mai dozes off, Harry asks Morgan to share what he was going to say earlier. Morgan refuses and Harry turns to see Murphy opening the door. He hastily pulls her back and she says that she saw her father out in the darkness. Harry points out that her father Jim lives in Florida, and Murphy admits that she hasn't talked to him in over a year and isn't sure if he's dead. She complains that she's useless and Harry points out that she got Morgan to talk. He suggests that she figure out who the mole is.
As Murphy agrees, Harry notices that the darkness isn't seeping through the window and talks to Morgan privately. He asks why the Warden doesn't simply teleport out, and Morgan reluctantly demonstrates that he can simply make himself imperceptible. Harry suggests that they shield themselves and just walk out. They meet with the others and Harry produces seven shielding bracelets. He warns them that they will only last a few seconds and Morgan suggests that they send out a scout to gauge the thickness of the barrier. When Harry points out that the darkness kills any living being, Morgan reminds him about Bob. Bob isn't thrilled with the idea but agrees. As they go to the door, Bob tells him that he hasn't found out anything by spying on the others. Harry assures him that he has a spell prepared to summon Bob back if he's gone too long. As they go to the door, Murphy thanks Bob for being brave and he smiles and asks her to wish him luck. She does and Bob steps out into the darkness. When Bob doesn't return, Harry tries to summon him without success.
An hour later, Murphy checks on Harry, who is at the back door waiting for Bob to come back. As they talk, Harry's father appears out of the darkness, trying to warn his son. Murphy figures that it's an illusion and something that they shouldn't trust. Amber calls to them that Bob is back. They run to the front room and Bob tells them that whatever is out there is more powerful than he is. When Morgan wonders how thick the field is, Bob explains that the person responsible shifted the building itself to The Other Side.
As they wait, Morgan puts on one of Harry's records and talks to Murphy. When she wonders how long he's known Harry, Morgan explains that they first met shortly after Harry's father died, and admits that Harry has been nothing but trouble because of his family bloodline. He then tells Murphy to be quiet and let him think.
In the kitchen, Harry approaches Amber as she looks for something to eat. She tells him that that she's not the traitor, but admits that she and Wallace are the only strangers and thus the likely suspects. When Harry says that he hasn't ruled anyone out, Amber says that she figures that it's him. He says that he doesn't kill people but Amber points out that he killed Justin Morningway with black magic. She explains that there's a case file--required reading--on Harry.
Frustrated, Harry goes to the workshop and starts smashing things in frustration. The darkness starts seeping in and Bob warns his friend that they're running out of time. Colm Dresden steps out of the darkness, seemingly surprised that he made it. Bob advises to stay away from it and Colm agrees. Harry asks Bob to give them a minute alone and the spirit leaves. Colm says that the woman who sent him there wants Harry to know that there's a traitor in the building… and to kill everyone to eliminate the guilty with the innocent. Before he can explain further, Colm is pulled back into the shadows.
Harry takes his staff and goes back out to the main room. As Murphy goes to her friend, Amber yells at Wallace to stay away from Mai. Wallace throws her off the upper loft and then jumps down and fires a blast of energy into Murphy. Morgan draws his sword and Wallace draws his sais, insisting that it's one of them. Harry confirms that Murphy is okay, while Wallace says that killing the others is the only way to eliminate the guilty party. He attacks Morgan while Amber tells Harry to check on Mai.
When Harry gets upstairs, Mai complains that someone is keeping her from healing... someone close. She suspects that it's Harry and tells him to try harder to protect her. A shot rings out and Harry looks down to see that Murphy has shot Wallace through the heart. Shocked, she wonders why she shot him, telling Harry that she doesn't kill people. Harry reassures her that Wallace was trying to kill them and she stopped him.
Morgan brings Mai downstairs as the lights flicker. The darkness flows over the upstairs loft and Morgan wonders why it moves, stops, and moves again. Harry tries to work out what is holding it back and realizes that it's Mai. The weaker she gets, the faster it closes in, and it keeps moving to spots that she leaves. Harry figures that Mai is controlling it, and retreated to his building and then sealed it off so that she could heal. Morgan points out that she isn't healing and Harry figures that something is blocking her abilities. The creature weakening her has to be close, and Harry figures that he invited it in so that it didn't set off his mystical alarms.
Harry turns to "Murphy," who smiles smugly and says that it took him long enough. She breathes out a burst of green flame and Harry blocks it just in time, and Morgan uses his sword to generate a shield. The creature tells Harry that Morgan knows what it is, and complains that Harry has chosen the wrong side. He has no idea what it's talking about and the creature says that Mai only cares about power. Morgan denies it and the creature tells Harry that if he kills Mai then it will let him live.
Morgan remains silent when Harry asks what they're dealing with, and the creature continues breaking down the shield. The Warden finally says that they're facing a drake, a shapeshifting immortal creature. The drake, growing impatient, reverts to its natural form and advances on the shield. Harry tells Morgan to pull it in tight while he makes Mai sicker in the hopes the darkness will close in. When the shield drops, the darkness consumes the drake and the three of them pour all the healing magic they have into Mai to bring her back. She wakes up, heals herself, and returns the building to the real world. Even Morgan is forced to concede that Harry did a good job.
Afterward, Amber apologizes to Harry for misjudging him. As Mai leaves, Harry asks if that's it, pointing out that two people died. Mai explains that she knew the drake was inside with them and she was willing to trap them all with the creature and die with it if necessary. As she leaves, Harry points out that the drakes are immortal shapechangers... and so is Mai. He doesn't ask the obvious question and Mai congratulates him on having the common sense not to.
As they go, Murphy arrives and comes in before Harry can refuse her access. She tells him that there was an explosion and asks if he knew anything about it. Harry says that he doesn't and refuses to introduce her to Mai and the others. Once they're alone, Harry tells Murphy that she's better off not knowing what happened and asks her out to lunch. She agrees and suggests that they go to the Golden Dragon for Chinese. He quickly suggests Greek instead and they leave.