Galactica stumbles upon Kobol, the long-lost home world of humanity that the 13 Tribes came from, which legend says holds the only clues to the location of Earth. Roslin convinces Starbuck to steal the captured Cylon raider and return to Cylon-occupied Caprica with it to retrieve a religious artifact that will unlock the secrets on Kobol.

Infuriated that Roslin usurped his command by ordering Starbuck to steal the captured Raider, Adama decides that his only option is to storm Colonial One with marines and terminate her presidency. Starbuck reaches Caprica and finds the Arrow of Apollo in a museum, but she has to go through a copy of Number Six to get it.

As the premiere for the second season unfolds, Adama lay dying leaving Tigh in command. Lee and Roslin have been sent to the brig. An emergency jump goes wrong leaving the Galactica alone in space without the fleet.

A Cylon virus is interfering with Galactica's power supply, while Cylon centurions are heading for crucial systems. Somehow they must be stopped.

Tigh has problems with the responsibility of being a leader, president Roslin loses control without chamalla. The Kobol team discovers a Cylon battery.

While Tyrol decides to start building a new fighter, the Cylon virus is rearing its ugly head again. Boomer says it means a large Cylon attack is imminent.

The secret source in the administration has provided Tyrol with a list of all humans scheduled for extermination. Tyrol's wife Cally is on the list and he sets off to rescue her. Sharon Agathon has made it safely to the planet but they are ambushed by Cylons lying in wait. They realize they were betrayed and Anders finds damning evidence that points to the identity of the traitor. D'Anna Biers has been having strange dreams of late and an oracle tells her that the child Hera is alive and she will hold her in her arms. Roslin meanwhile assigns a squad of men to protect the child at all costs. The Admiral sends the Pegasus away with the few remaining civilian ships to continue the search for Earth.

Now safely back in the fleet, those who managed to escape from New Caprica are seeking revenge against those they believe collaborated with the Cylons. Six of them, including Chief Tyrol and Col. Tigh, have formed the Circle and are acting as judge, jury and executioner. Those found guilty are blown out of an airlock. Lee Adama has noted that in the three days since everyone was reunited, 13 people have simply disappeared without a trace. The morale aboard the Galactica is not good with perceived collaborators being shunned by the others. Among those in that situation is Felix Gaeta who, as Gaius Baltar's Chief of Staff, is high on the Circle's list. As for Baltar is now being kept aboard a Cylon Basestar and his captors are deciding his fate as well.

The Chief and his wife get trapped in an airlock on a routine maintenance job, while the Admiral copes with his wedding anniversary and the memories of his ex-wife.

When the head of the fuel production plant holds the fleet hostage by providing unsafe fuel, he's arrested for treason, which results in the Chief sent to the ship and held responsible for getting the plant back up and running.

Baltar goes on trial for his life, and it affects everyone from Lee on up to the president.

Coincidences creates new alliances aboard Galactica.

During a seemingly hopeless battle, Kara Thrace appears in a pristine Viper, claiming that she has been to Earth and can lead the Fleet there -- but the terminal Laura Roslin believes otherwise. Meanwhile, four of the so-called Final Five are forced to tackle the repercussions of their newfound nature, while Gaius Baltar discovers he has a commune of nubile female cultists who believe him to be an agent of the "one true God".

Starbuck (Katee Sackhoff) and Laura Roslin (Mary McDonnell) face off with a gun between them, Lee Adama (Jamie Bamber) says goodbye to the Galactica, violent conflict breaks out between the seven models aboard Cylon Basestar, and Gaius Baltar (James Callis) is directly pulled into the "Final Five" situation.

The aftermath of a coup among the Cylons leads to further violence, Lee finds himself facing off against Roslin during his first meeting with the Quorum of Twelve as the new representative of Caprica, and Cally discovers the horrible truth about her husband Galen Tyrol. Meanwhile, Starbuck aimlessly searches for Earth with Anders and other Galactica officers.

When a Heavy-Raider manned by Leoben Conoy docks aboard the Demetrius, confrontations form between the crew over the possibility of a truce with Cylon rebels, while Starbuck puts her trust in an old enemy.

A vicious injury ends the mutiny attempt aboard the Demetrius, Kara leads her crew to the Cylon rebel's Basestar, and Roslin begins to understand Gaius Baltar's appeal to his followers. Meanwhile, Anders attempts to secretly find answers to his purpose as a member of the Final Five.

A shaky alliance between the Colonial Fleet and Cylon rebels is put to the test when the two groups combine efforts to take out a Cylon "Resurrection Hub". Meanwhile, Athena loses control when Hera becomes unnaturally drawn to Natalie.

The Hybrid keeps jumping the basestar, and Roslin has visions. The three, D'Anna, is un-boxed. Humans and Cylons engage in a battle to destroy the Resurrection Hub. Baltar is badly wounded and Roslin has to decide whether or not to help him.

Scouting the planet reveals that there is no life except plants. The destruction occurred about 2,000 years earlier. Among the ruins, skeletons and wrecks of a different kind of Centurions are found. But closer examination of the skeletons reveals they are Cylon! Could the 13th Tribe really have been all Cylons? Chief Tyrol, Colonel Tigh, Sam Anders and Tory remember living on the planet and dying there. How did they get to the colonies? Starbuck finds a piece of her Viper, and despite Leoben's warnings, starts to look for the cockpit... Roslin loses her faith in the Scrolls of Pythia. Apollo and Dualla seem to get back together, but he needs to figure out what to tell to the people of the Fleet... A tragedy prompts Adama to confront Saul.

The Fleet refuses to cooperate with Cylon engineers and Adama decides to put an end to it. He sends the Quorum a message stating that unless they wish to join Zarek in the cell, they get their people in line. However, Gaeta has already freed Zarek with the help of other would-be-revolutionists. They allow Zarek to leave Galactica on a raptor. He lands on Colonial One and enters a gathering of the Quorum. Meanwhile, Anders gets ambushed and captured. At the CIC, Gaeta cleverly manipulates everyone else until the time is at hand for the revolution to begin.

Roslin is on board a raptor en route to the Rebel Cylon Base Star, but Gaeta has ordered to engage and destroy it. The marines have used a stun grenade on Adama and Tigh. Roslin manages to get a wireless transmission out for everyone to hear and learn what Gaeta has done. She and the others barely make it to the Base Star, where she convinces Tory and the other Cylons to use the Fleet as a cover in order to prevent Gaeta from attacking it. She also believes that Adama will be able to save the rest of the Final Four. Temporarily safe, the Rebel Cylons start voting on whether they should just jump away and count their losses. Adama is brought before Gaeta and Tigh is thrown to the brig with Caprica Six, Anders, Athena, Helo and their child Hera. Zarek comes aboard Galactica on Colonial One with the Quorum. At Gaeta's insisting, Zarek agrees to put Adama on trial for treason, with Romo Lampkin assigned as his defence lawyer. There's just one problem: The Quorum refuses to recognize Zarek's authority. However, Zarek is hell-bent on following his "The truth is told by those left standing" maxim. Only Tyrol, who's alone, and Lee, whose with Starbuck, are Galactica's last hope.