This is the Way the World Ends is the season finale of the 6th season of Dexter. The episode originally aired on December 18, 2011 (2011-12-18).
Dexter and Homicide race against a solar eclipse to catch the Doomsday Killers before their final gruesome act; Debra struggles with a new emotional reality.
Dexter is adrift in the ocean, alive and unburned, clutching a piece of the lifeboat. When that makeshift float sinks, he thinks about what knowing he is going to die feels like.
Just then a ship happens by. It seems to be a group of people trying to get into the U.S. illegally. The owner of the boat pulls out a gun and starts to rob everybody. Dexter reacts quickly, taking a huge fishing lancer and kills the man. He takes control of the boat and brings everybody near the shore.
Travis is still in the home of the couple he killed. On TV we see that a solar eclipse will take place the following day.
Dexter tells Jamie that he fell off his boat while out at sea. She reminds him that Harrison's pageant is tomorrow.
Travis breaks apart furniture and piles it in the middle of the living room. He says "Today's the day" and leaves.
An emotional Deb hugs Dexter. She heard his boat had washed ashore and was worried he was dead. She says "I love you" and he off-handedly says "I love you, too." She says "You do?" and says she doesn't think he's ever told her. They get word of a double murder.
It's the couple Travis has killed. Dexter is the first one inside which gives him the opportunity to remove his face from the huge tableau Travis had painted in the living room. The rest of the team comes inside. They figure out the painting is the beast in the lake of fire, and wonder if it's the final tableau. Deb is acting strangely around Dexter. After she leaves Dexter spots a hand-written drawing in the trash. He wonders if Travis's work isn't finished after all.
Travis drives by and sees the police have shown up. He wonders what to do next, then looks down at Dexter's license in the wallet he had taken after incapacitating Dexter, and says "Thank you."
Louis asks Masuka about staying around permanently. Masuka mentions part-time work might be possible.
Deb shows the team that the night before a pilot took a picture of a circle of fire about seven miles off shore (the one set by Travis to surround the dinghy he'd left Dexter in). They think that means Travis has completed his work. The working guess is that Travis will want to watch the eclipse (the end of the world) from a high point, which in Miami means a skyscraper. Deb wants to post uniform officers at the top of the city's tallest buildings.
Based on the sketch Dexter found he decides Travis will most likely be going to the Transcorp Building, which is solar powered. Deb asks Dexter to do a final sweep of Travis's church after Harrison's pageant. She asks Dexter if they need to talk but he doesn't seem to know what she's talking about.
Angel tells Quinn he's going to transfer him out of Homicide. Quinn isn't happy.
Much to Deb's surprise LaGuerta accepts her idea of targeting the skyscrapers in order to find Travis.
Using Dexter's keys Travis lets himself into Dexter's apartment. There is a package left (delivered) at the front door addressed to Dexter which Travis brings inside with him. After changing his shirt with one of Dexter's shirts he opens up the box and pulls out the Ice Truck Killer's prosthetic arm Louis anonymously sent to Dexter. Puzzled, he places the arm back in the box and leaves it on top of the fridge as he hears Jamie come from the other room getting ready to take Harrison to the pageant. He learns that Dexter has a son and spots a flyer for the pageant.
The way the pageant is organized, each parent leads their toddler on stage wearing a mask of the animal their child is dressed as.
Deb gives final instructions to the officers that will be looking for Travis. Quinn tells Angel that he's told his union rep that he has an alcohol problem. Since it's a disease, as long as he seeks help he cannot be fired or transferred.
Looking at one of Gellar's drawings and going back to some old pictures they suspect that Travis may not be done killing. Deb calls Dexter and says that before the eclipse (which is less than an hour) Travis will offer a sacrifice. Since a lamb was used in the drawing she thinks it could be an innocent of some kind. Dexter realizes he can't find Harrison. A woman tells him that Harrison "just left" and we see Travis leading Harrison towards the Transcorp Building.
Using Harrison as a distraction Travis is able to kill the cop posted on the building's roof. When Deb checks in with the various buildings Travis grabs the radio and says "all clear."
Travis pulls out a sword and holds Harrison in his arms. Just before killing the child Dexter runs up and tells him to stop. Since "the beast" isn't dead, Dexter argues, sacrificing an innocent won't work. Dexter gets Travis to agree to release Harrison as long as Dexter injects himself with the hypodermic he's brought. But Dexter doesn't actually push the plunger and turns the tables on Travis just as he is about to kill him. He knocks Travis unconscious and grabs Harrison.
When the Transcorp officer stops responding the teams head over. They find the officer dead. They find an altar, but no sign of Travis. Deb is panicking. LaGuerta shows up but assures Deb that she did the right thing.
Dexter gives Travis another tranquilizer shot and locks him in his trunk. He puts Harrison to bed.
Deb barges in to see her psychiatrist without an appointment and blurts out that she realizes she's in love with Dexter. She thinks that is the explanation for why she's chosen some terrible men. She's been trying to hide from her feelings. Her plan is to tell Dexter how she feels and find out what he thinks.
Travis wakes up on Dexter's slab in the abandoned church. Travis makes the case he was chosen by God to bring about a new world. Dexter counters that all Travis was doing was using God as an excuse to kill innocent people. Dexter says light cannot exist without darkness and perhaps his darkness is to bring balance to the world.
While Dexter is talking to Travis we see Deb walk through the church doors by herself. From a distance she sees Dexter plunge a knife into Travis's chest.
At that same moment Dexter turns his head and realizes his sister has seen him murder Travis.