Previously: The fleet finds an inhabitable planet, which they find out is Kobol. A survey party heads toward it and is shot down by Cylons. Adama decides that before they send a rescue mission for the downed Raider, they need to blow up a Cylon base star orbiting around Kobol, using the Cylon Raider that Starbuck recovered earlier in the season. Roslin has other ideas, and gets Starbuck to take the Raider and head back to Caprica to recover "The Arrow of Apollo."
On Kobol: The crew of the downed Raptor, which includes Crashdown, Chief Tyrol, Dr. Baltar, Cally, and a couple of expendible people, escape the ruins of their crashed ship. Imaginary Six once again helps guide Baltar out of danger. He collapses on a hillside.
Meanwhile! On Cylon-Occupied Caprica: Helo and Boomer #2 are staking out a history museum. Helo doesn't understand why, Boomer explains about the Arrow of Apollo and how it's in the museum and it's totally important. Helo wants her to shut her yap, but she points out (correctly) that she's the one who's been keeping him alive this whole time.
Furious that Starbuck has run away with his Cylon raider, Adama decides to take his anger out on Roslin, citing her sending of Starbuck on the Arrow of Apollo Mission as an act of treason. He asks for her resignation, and when she refuses, he tries to remove her from power. Roslin counters by letting him know that the press core has been listening in on the whole conversation. Adama hangs up, then orders a strike team to hit Space Force One.
On a roll, Adama insists Boomer #1 go on a suicide run to blow up the base star. Which is totally cool, because she just tried to blow her face off in the last episode. There's one Cylon transponder left, which he wants to place aboard her Raptor so she can get near the base star, fire off a warhead, and scurry away.
Meanwhile! On Cylon-Occupied Caprica: Starbuck shows up in her Raider, looking for the Arrow of Apollo. Boomer #2 reveals to Helo that she's pregnant.
The strike team heads out to Space Force One. Lee and Tigh are on it. Boomer heads out with "Racetrack," (because Crashdown is stuck on Kobol) towards the Base Star. As Roslin is telling her assistants and advisers that they should hide in the cargo hold, the strike team lands on Space Force One.
Back near Kobol, the suicide mission with Boomer #1, The Original Sharon, is going great -- until a missile misfires. She decides to fly her spacecraft right into the Cylon base star, and detonate the warhead manually. (Because why try to shoot your face off again, when you can just blow up yourself and a whole lotta robots, too?)
On Kobol, Crashdown is pulling rank and acting like a moron. Tyrol points out that they can't go to high ground to be seen by a rescue party, because they'll also be seen by the Cylons.
Dee and Billy, like two kids caught in the middle of their parent's divorce, are acting as go-betweens for their respective bosses. Adama insists that he's going to take Roslin out of power, by force if he has to, and she won't back down, so the strike team boards Space Force One.
Meanwhile! On Cylon-Occupied Caprica: Starbuck finds the ruined museum, and the Arrow of Apollo. A copy of Number Six attacks her. Starbuck beats the Cylon by jumping on her and falling a couple floors. Helo and Boomer #2 show up.
While aboard the base star, Boomer runs in to several (naked) copies of herself. They're all smiling and saying "We Love You, Sharon!" which is creepy, and rightfully freaks out Boomer. Or, maybe she's freaked because she finally realizes that she really is a robot. Either one is creepy. She takes off, and they detonate the warhead. No more base star.
The strike team lands, and Lee objects to all of this resignation business, so he pulls a gun on Tigh. This is seen as an act of mutiny, so when Roslin finally talks Lee into putting his gun down, both he and Roslin wind up in the brig.
Boomer makes it back to Galactica alive, foiling any plans she had to kill herself. Maybe now that she knows she's a robot, she plans to get some informational literature to help herself explore the "cybernetic side." It's not a lifestyle choice!
Meanwhile! On Cylon-Occupied Caprica: Starbuck sees Boomer #2 and realizes that if Boomer #1 is on Galactica, then this Boomer is some other Boomer.... and that all Boomers must be Cylons -- so PUT YOUR HANDS UP, ROBOT, I'VE GOT A SPACE GUN! Helo stops Starbuck from killing Boomer #2. But just barely.
On Kobol: Baltar envisions himself and his imaginary girlfriend Number Six in front of a crib. Six tells Baltar it's their child, and also it's "the shape of things to come." This is where half the audience gets lost in its own reasoning -- if Six knows about Caprica Boomer's baby, is she real? She's not part of Baltar's imagination? Baltar's unconscious has no way of knowing that Boomer #2 is back on Caprica, pregnant, right? Or, wait. Is he a sleeper agent, too? GAH!
It's all high-fives and accolades on the Galactica until Boomer #1 takes out her sidearm and shoots Adama a couple times in the chest. The first season ends on a slow-motion montage of Adama bleeding all over the Combat Information Center.