Dexter is putting everything together with respect to Travis and Gellar. Dexter looks at Gellar's body and sees that he was killed by the same sword that was used in the earlier "Doomsday" murders. Travis looks down at Dexter in the basement and locks the trap door. Dexter watches through the bars as Travis talks to himself, thinking he's speaking with Gellar. Gellar is telling Travis that he killed him several years ago when the professor didn't agree with Travis's strange ideas. Travis says he doesn't need Gellar anymore and is going to make "new disciples."
Dexter tells Harry that Travis can't be saved. He finds a way out of the basement and sees that Deb and the department are closing in on the IP address and will soon find the church. Dexter cuts off one of Gellar's hands and uses it to plant fingerprints to make the cops think Travis wasn't working alone. He then removes Gellar's corpse.
Dexter goes to Travis's hotel room and uses his laptop to post as Gellar on his blog: "I was wrong. This was all the Devil's errand. I'm sorry I misled you."
In a computer lab Travis reviews videos of supporters from the blog. He stops on one from a man named "Doomsday Adam." His name is Steve Dorsey and Travis sends him a message that they should meet. Travis also responds to Dexter's post, writing to the "False Prophet" that "You're not fooling anyone."
The cops finally arrive at the church and realize that this is where everything happened. Deb seems to be bothered by the place and has to take a step out for some air, avoiding an apparent panic attack.
Quinn wakes up in his car after yet another night of heavy drinking.
Dexter gets to the church and finds Deb outside. He thinks she's having a panic attack and helps talk her through it. Inside Dexter looks for clues to help him find Travis. They see a painting of the next tableau, "The Wormwood," something about poisoning mankind.
Deb gets a call from Chief Matthews, who wants to set up a dinner.
They find a prescription bottle for Travis. On his phone Dexter sees that Travis is talking to him on the blog. He refers to "fixing a mistake."
Louis tells Jamie he wants to show Dexter his new video game. Jamie assures him that Dexter is a softie at heart.
Maria is trying to "help" Deb by leading the latest department briefing. Eventually Deb asserts her will as her Captain falters and effortlessly assumes control of the meeting. They talk about Holly and drinking blood. Dexter wonders if she is the mistake Travis will want to fix.
Travis goes to visit Dorsey and his wife Beth and they are thrilled to meet him. He tells them their "time has come," and he needs to know that they are fully committed.
Dexter goes to Holly Benson's apartment and finds an address he thinks could be a boyfriend. The man's daughter tells him that Holly could be on her father's yacht as the father is away on business.
Holly is on the yacht telling a friend she's going to crash there. Travis, Dorsey and Beth show up and grab her, calling her "Whore!," then take the boat out into open water.
Angel warns Quinn about the way he's been acting. He thinks he needs to suck it up and start acting like an adult. Anderson brings over Travis's psychiatric file. He has a long and disturbing past, that includes breaks with reality and possibly murdering his parents. Dexter learns the name of the boat Holly is using online.
Deb talks to her therapist, Michelle Ross, about her trouble in the church. They think it might be because she associates churches with funerals and loss.
Travis coaxes Dorsey and Beth into helping him kill Holly.
Louis Greene shows Dexter his new video game, which allows users to play as their choice of notorious serial killers. Dexter very directly tells him it's a terrible idea. Louis gets so upset he leaves, blowing off a date with Jamie.
Dexter gets access to security footage at the marina and sees that Travis did take out the boat. He finds the yacht's GPS tracking info and uses it to learn its current location.
A hazmat-wearing Travis finishes making his wormwood poison.
Deb uses her detective skills to figure out that Chief Matthews sent flowers to Jessica Morris the day she died. She wants to talk about this development with Dexter, but he won't be in until later.
Louis gives Angel an address for Dorsey, who has been posting strange videos on the blog.
Angel can't get Quinn on the phone. He goes to Dorsey's home alone.
Dexter sees someone on the yacht in a hazmat suit. There is a violent struggle and Dexter ends up stabbing the other figure in the chest. It turns out to be Dorsey, who, as he expires, tells him "You're too late. Wormwood can't be stopped."
At the Dorsey's, Beth tells Angel the whole thing was a joke. But on his way out of their house he notices a shelf full of Gellar's books. Just as he realizes what is happening Travis appears behind him and hits him over the head with a cross. Travis picks up Angel's badge and says "Miami Metro Homicide: That's where God wants us to stage Wormwood."
Dexter finds Holly's body on the yacht's anchor in the water. She was stabbed. Harry wants him to call the police, but Dexter wants to fix the problem himself.
But when Dexter sees the materials used to make poison gas, he picks up the phone and anonymously reports the gas and the boat's location.