The Enterprise's plan to destroy the Borg ship with a specially directed frequency of energy from the ship's main deflector dish fails when it turns out Picard's knowledge of the clever plan has been passed to the Borg and has allowed them to prepare a defense against it. "Your resistance is hopeless, Number One," says Locutus. The Borg proceed on their course to Earth as the Enterprise sits helplessly awaiting repair.
The episode's biggest plot conceit, obviously, is that the Borg don't destroy the Enterprise or assimilate its crew right then and there. Not being a threat, the rationale is that the Borg decide to simply ignore the non-threat and proceed to Earth. But come on. Obviously, the real reason is that it's the only way to permit the story to move forward. Granting the constraint that Picard and the Borg and the Enterprise must all survive the legendary "Mr. Worf, fire" setup, part two proves surprisingly effective as the solution to what seemed like an unsolvable problem. It's not an exercise in rock-solid logic, but it is an exercise in compelling TV.
The tension that was evident in the first part of the story does not for an instant wane here. The Borg are still headed for Sector 001, Starfleet is still woefully unprepared for the battle, and Picard is still in the clutches of the Borg. In an intriguing scene with harrowing implications, we see Picard being further transformed into Locutus; a streaking tear reveals that beneath Locutus still exists Picard, in torment. Aboard the Enterprise, Picard's absence fuels a solid character story for Riker, who must assume the role of captain under the worst possible circumstances and simultaneously step into Picard's shoes (and out of his shadow) for his crew while squaring off against Picard as the enemy. Guinan, who offered words of wisdom to Picard in part one, now bluntly tells Riker that he must let Picard go in order to do his job.
Meanwhile, the Borg march toward Earth. Starfleet's desperate stand at Wolf 359 ups the ante on the foreboding, and when the Enterprise subsequently arrives upon the debris of the wiped-out fleet, it's a particularly striking scene.
The secret to this story's success is its careful balance of elements and that it never loses sight of the fact that this is a TNG show, even amid the chaos. In addition to showing how the crew reacts and plans for this looming threat, Michael Piller's script keeps the story humming along on all cylinders; the details follow on the Borg ship, at Starfleet's desperate stand, and as Riker must hatch a daring plan to retrieve Picard from the Borg. This leads to some of TNG's most memorable action, in which Picard is retrieved but not rescued (the crew has his body but has not freed his mind). The show then shuttles into pure TNG problem-solving mode, in which the crew must figure out how to save Picard and stop the Borg, which might be one and the same.
Given that the story must resolve itself and Picard must survive, the solution is a clever one that allows the Borg to be defeated but without the brute force that part one had assured us was not possible. I find it highly unlikely that the access to the Borg's "sleep" system would not be under higher security, and even more unlikely that a self-destruct fail-safe would automatically ensue after that. But what the hell — the execution of the plot and the struggle and Picard's angst depicted in Data's hacking scenes bring it home as drama.
The show wisely keeps Ron Jones as the composer, bringing a musical continuity to this two-parter in a way that is more crucial than in virtually any other multi-part Trek on record.