Chain of Command is one of my favorite, and most disturbing episodes of TNG ever. After the Cardassian captor relates the story about growing up hungry and abused when he was six years old, Picard, half-dead, manages to say:
“Despite all you have done to me, I still find you a pityable man.”
Shit.
Anyhoo, I have all the TNG episodes on DVD, so I will attempt a detailed synopsis of what happens during Best of Both Worlds.
In the first half, the Borg beam directly onto the bridge of The Enterprise and fight some of the crewmen. In the midst of the shenanigans, one borg grabs Picard, injects him with some nanites and they all beam back to the cube. There, his assimilation is begun (it takes a lot longer than it did in First Contact). He begins talking to the Enterprise about being Locutus and stuff.
In the second part, Riker et al realize they can’t use any of the battle plans they discussed with Picard because now the Borg now all about them. Also, they can’t beam Locutus out of the cube because of the Borg’s shields. So Riker orders the saucer to be seperated and starts shooting at the cube with the battle-section. Meanwhile, a shuttle with, (I think) Data and Worf is launched from the saucer section. The shuttle drives through the Borg’s shields (on momentum only, to prevent leaving a sensor trail) and then they beam into the Cube to find Locutus. They grab him and transport back to the shuttle, which drives out of the Borg’s shields, then they transport back to the Enterprise just as the Borg blow up the shuttle.
Once there, Beverly determines that she could remove the Borg implants, but not while Picard’s brain was still connected to the collective, as that would probably kill him. Data decides to try to hook himself into Picard to access the collective so they can learn about it. Data tries to implant commands to power down or disable the weapon systems, but all the essential command divisions are protected by access codes that Data cannot crack.
Just then, Troi senses that Picard, not Locutus, is trying to communicate with Data. Picard says, “Sleep, Data, sleep.” Data interprets this as a cue to implant a command to the collective to enter their regeneration cycle. This command is not protected by an access code and it works; the cube shuts down just before attacking Earth. The Cube, realizing there has apparently been a malfunction, self-destructs.
Once the cube blew itself up, Picard’s mind is free and Beverly can remove the implants.
Later on in First Contact it seems that Picard was never fully removed from the Collective, as he can sense them coming and Data is able to contact him via the Borg mind at the end of the second act.