On Arcta, the assault team, led by the Thetas, manages to evade the Cylon patrol. They learn that the Thetas were created as slave laborers and they hate the Cylons. The Thetas enter the underground city.
S5-9 agrees to take Apollo to Dr. Ravishol. On Baltar's base ship, Lucifer reports that the Galactica's probe managed to land on Arcta. He orders the fighters to attack the Galactica again. The Cylons begin searching the city for the humans so Tenna is told to take the team to where they are hiding their children. S5-9 takes Apollo to see Dr. Ravishol but he accepts no responsibility for the Cylon's misuse of his technology. A Cylon squad arrives at the lab to search for the humans but the doctor manages to hide Apollo before he allows them inside. The Cylons take S5-9 for punishment and leave.
The Cylons arrive at the area where the Theta's are hiding their children but only do a cursory search before leaving. In the lab, Apollo tries to convince Dr. Ravishol of the Cylon's true motives. He tells the doctor that the Theta's are thinking and breeding. Ravishol is astonished to learn that they have children. Baltar's fighters attack the Galactica and are repulsed by the Galactica's vipers. On the base ship, Baltar orders his fighters to break off their attack in an effort to lure Adama into thinking his base ships are closer than they are. At the lab, Ravishol tells Apollo that the gun must be attacked at the same time as the garrison and shows him where to place the charges on the cannon to destroy it. Thane dons a S-5 uniform and slips away from the others. Tenna arrives at the children's hiding place with the team when Boomer notices that Thane is missing. Tenna and her sister go looking for Thane. Thane is captured by the Cylons and Starbuck convinces Tenna that he needs to find Thane before he betrays them to the Cylons.
Unable to get information from Cree, he is placed into a cold cell for further study. Starbuck and Tenna find a battered S5-9 who tells them that Ravishol is helping them. As they watch, Thane is interrogated by the Cylons but he manages to get them to activate his hand-held bomb killing him and several Cylons in the process. Starbuck returns to the group and Apollo is waiting for him. He gives Starbuck the responsibility of destroying the Cylon garrison while he goes after the pulsar. Theda and Wolf finally convince Croft to escape with them when they reach the Cylon fighters at the top of the plateau. On the base ship, Lucifer reports that some of their fighters have enough fuel to return. Baltar orders them to re-engage the Galactica. Apollo's assault team is trekking up the mountain top in blizzard conditions. The Cylon fighters renew their attack on the Galactica. The fighters retreat as three base ships close on the Galactica. The Galactica orders the fleet to increase to flank speed. Baltar contacts Arcta and orders the pulsar to begin random firing. The pulsar blasts trigger an avalanche and Apollo saves Croft from certain death. A crew member's leg is broken and Apollo asks one of the Thetas to take him back down the mountain.
The pulsar continues its random firing as the blasts get closer and closer to the approaching fleet. Apollo's team reaches the summit of the plateau. Theda and Wolf decide to make a break for it but before they can kill Apollo, the pulsar fires again and Wolf and Apollo grapple. Apollo grabs his laser and Wolf runs off into the blizzard. Croft convinces his wife to help them destroy the pulsar and Apollo puts Croft in charge of the team. Tigh recommends that all ships proceed at their best available speed so that some of them have a chance against the pulsar. On the garrison assault team, Starbuck goes with Tenna to rescue Cree over the objections of Boomer. Apollo's team prepares to enter the intake tube of the pulsar. Starbuck enters the cold cell area and frees Cree. Tenna tells Starbuck that the Thetas will help them destroy the Cylon garrison but they will not allow the pulsar to be destroyed. Apollo's team locates the firing station with the targeted energy pump that will destroy the pulsar. S5-9 refuses to let them destroy the pulsar but Ravishol intervenes telling them that he will protect them from Cylon retribution.
As the Thetas leave to help them destroy the pulsar, Ravishol tells Starbuck that he didn't give the Cylons everything that he created. Starbuck's team places their charges at the garrison. Apollo's team attacks the firing station. The Cylons at each place are killed. Croft and Theda begin placing charges on the energy pump when a Cylon enters the chamber. It fires at Croft but Theda pushes him out of the way and is killed. Starbuck then enters the chamber and kills the Cylon as the rest of his team enter. The two assault teams leave the area and Starbuck gathers up Boxey and the Theta children. As the countdown ends, the cannon is fired just as the pump explodes and the whole top of the mountain is destroyed. The Galactica notes the location of the surface blast and amid the celebration, Adama orders a rescue unit with full fighter escort to the surface to retrieve their assault force. On Baltar's base ship, Lucifer reports that the pulsar has been destroyed and that the fault lies in Baltar's hands not his. He suggests that they come up with some sort of united front for explaining the debacle to the Imperious Leader. On Arcta, Ravishol is surrounded by all of his children as Apollo says his goodbyes. Starbuck is also saying goodbyes (with kisses) for each of the Tenna models.