This was the fourth episode of Season 2. Colonel Tigh is still in command of the fleet after declaring martial law. When other ships refuse to supply Galactica in protest of Tigh's actions, he sends the Marines to the Gideon to obtain those supplies by force if necessary. The situation quickly gets out of hand and four civilians are killed in what is later described as "The Gideon Massacre."
Tigh also had Tyrol arrested after his return from Kobol because of his relationship with Sharon ("Boomer"), who was previously revealed to be a humanoid Cylon.
After the Gideon incident, Roslin conspires to escape from Galactica with the help of Lee... and Tom Zarek.
On Caprica, Helo and Starbuck encounter members of the pyramid team, the Caprica Buccaneers, who have been staging hit-and-run attacks on the Cylons ever since the initial Cylon invasion.
At the end of the episode, Cally avenges the deaths on Caprica and the rest of the Colonial homeworlds.
I thought this was another excellent episode. Even more political tension, some exciting gunfights on Caprica and another surprise ending. I wasn't expecting that to happen although I did fear an attack on Boomer when she was being led down the hallway.
The internal divisions among the humans in Season 1 have now become complete in this episode. President Roslin, Lee Adama and Tom Zarek have literally and figuratively split from the command of Galactica. The instability of the situation helps to show the importance of having a powerful commander like Adama at the helm.