The second part evens out the roles of the two leads a bit more, with some memorable scenes for Sheridan and an aged Londo, and the final revelation of Sinclair's much-hyped "destiny."
Sheridan is still unstuck in time, having been propelled forward 17 years to the future of Centauri Prime. In this future, Sheridan and Delenn are married with a son... but they are also prisoners of the Centauri Emperor: an aged, drunken, embittered Londo Mollari. It seems that Sheridan and Delenn won their war against the Shadows but, in Londo's words, "neglected to clean up (their) mess!" Allies of the Shadows infiltrated Centauri Prime and left the planet in chaos. The cities outside the palace burn, and Londo bitterly implies that the fault lies with Sheridan, whom he sentences to death.
Meanwhile, in the story's present, Sinclair, Delenn, Ivanova, and Marcus have infiltrated Babylon 4. They successfully stabilize the station and bring it forward to the year 2258, to allow 2258's Sinclair and Garibaldi to evacuate the station (Babylon Squared). But all this time travel has an unexpected side effect on Sinclair. Due to his past, unprotected exposure to the temporal rift, time travel ages him. The hop to 2258 has made him an old man. Another trip, back to 2260, is likely to be fatal...
If Part One was centered around Sinclair, leading to an odd feeling of an "arc" episode that revolved almost entirely around a guest character (albeit a guest character who was formerly the series' lead), then Part Two balances the scale with a lot more focus on Sheridan. Sheridan's subplot, in which he is unstuck in time and shot 17 years into the future to witness the fate of Centauri Prime, is not actually tremendously relevant to the main plot of this 2-parter. It has huge ramifications for the overall arc, though, as we glimpse the consequences of the current war on the future.
The scenes on Centauri Prime, with an aged Londo holding Sheridan and Delenn as condemned prisoners, are easily the best of the episode. There are wonderful dramatic riches here. We finally see the payoff to Londo's vision of his fate, reported all the way back in Midnight on the Firing Line. We see the moment in which Vir becomes Emperor, in a scene more than a little reminiscent of I, Claudius (and why not? Vir was obviously heavily modeled after Claudius to begin with). We also get to see a wonderful scene between Sheridan and Delenn, the first on-screen kiss between the two characters... which, as has been frequently noted by other reviewers, is all the more perfect because it is their first kiss for Sheridan, but not for Delenn. I also loved Delenn's observation, looking into Sheridan's eyes, of his innocence... an innocence that will be gradually lost in the future. Terrific stuff.
Much of the main plot is also quite strong. Given that this entire 2-parter basically amounts to iodine and bandages on the big, gaping chest wound left in the arc by Sinclair's premature departure, it's rather surprising how well JMS manages to make it all work. The "aging effect" that time travel has on Sinclair seems like a clear plot device to explain away "old Sinclair" from the end of Babylon Squared. Nevertheless, as presented in the plot, it is not difficult to accept. After all, we saw the potential effects of time distortion way back in Babylon Squared, when the ill-fated redshirt pilot was aged to death. Given that, and Sinclair's stated reason for leaving Garibaldi out of this mission, it is an entirely reasonable side effect (and, based on the outline in JMS' script books, would apparently have been used in any case, just not as a permanent effect).
Sinclair's ultimate fate may not have been the one originally planned for him, but it fits well with the general course of Season One's narrative, in which it was repeatedly hammered home that Sinclair had "a destiny." In fact, having read JMS' outline for the full arc with Sinclair, I actually think his fate here carries more dramatic resonance than the one originally intended. The use of quick flashbacks to Season One episodes such as Soul Hunter, Legacies, and Chrysalis to tie it all together is also effective.
I enjoy a good paradox, and this episode offers two. The first is the Chrysalis machine itself. Delenn transformed herself using the device, which was recovered from Valen when Babylon 4 arrived in the past. Sinclair transforms himself into Valen using the device, which he got from Delenn... meaning, since each was only able to use it because the other had used it first, that the device was apparently never actually invented by anyone!
The second potential paradox is Sinclair's letter. The letter from the past, written by Sinclair and addressed to Sinclair, tells him what he must do and brings him to Babylon 5 at the right time to do it. He still has that letter at the end of this episode, and apparently takes it to the past with him... meaning he never actually has to write it; all he needs to do when he arrives in the past is have it sealed back up in a vault, for himself to discover in another 1,000 years. (admittedly, here I'm probably overthinking... still, it's kind of fun).
Finally, this is the episode where Zathras really gets to shine as a character. Straczynski has written some wonderful lines for Zathras. I loved his scene with Susan, where he starts expounding on the infinite nature of time while rummaging through a toolbox. "Time is infinite. You are finite, Zathras is finite, this is wrong tool, never use these." All delivered by Tim Choate in exactly the same tone, so that Zathras gives just as much weight to the tool being wrong as to the nature of the universe. Perfection.
Even better is Zathras' reconciliation of various dropped plot threads and bits of confusion over who is "The One," by drawing on the Minbari society the show has created. I can't really say it any better, so I'll just transcribe the speech itself:
"All Minbari believe is around Three. Three castes: worker, warrior, religious. Three languages: Light, Dark, Grey. The Nine of the Grey council: Three times three. All is three... as you are three. As you are one. As you are 'The One.' You are the One who was, you are the One who is, and you are the One who will be. You are the beginning of the story, and the middle of the story, and the end of the story that creates the next, great story."
Some of his detractors have faulted JMS for his love of monologues. For myself? I think if you can regularly write monologues that reverberate like that, then you're just as well advised to stick with them. After all, Shakespeare was wordy too.
No matter how well-executed this 2-parter is - and it is very well-executed - there's no escaping the sense that it really does amount to iodine and bandages on a big, gaping chest wound. Comparing this 2-parter with Babylon Squared, the episode to which it acts as "the flip side," one can see many discontinuities. Some of these are quite minor; certainly, it is easy to observe that Zathras is discovered by the Babylon 4 staff in a manner different than that described in Babylon Squared, but this isn't something that particularly harms my enjoyment of the episode.
But there's one discontinuity which just irritates me. At the end of Babylon Squared, the reveal of the aged Sinclair provided the first season with one of its most memorable moments. As Sinclair sighed, with the heavy weariness of a man crushed by the weight of the universe itself, that he had "tried to warn them, but it all happened, exactly as I remembered it," I could feel the goosebumps rise on my arms. It felt clear that the warning Sinclair had attempted to make was huge, dire, as epic as the story of the series itself.
This episode would have me believe that the crushing weariness was felt because Sinclair was unable to warn Garibaldi to "watch (his) back." I don't buy it; I don't buy it for a second. And that particular discontinuity just briefly cheapens the memory of a truly great scene from the earlier episode (the staging of the scene also doesn't match up with the staging of the Babylon Squared scene, which likely has much to do with the changed nature of the Sinclair/Delenn relationship from the original plan).
On a more minor note, as with Babylon Squared, the Babylon 4 staff really aren't very good actors. I do think the Major Krantz actor is better here than he was in that episode, but he's still far from good. The rest of the B4 staff is even worse. Fortunately, they have less screen time here than they did in Babylon Squared, and so the damage they do is minimal.
So not quite as strong as Part One, but still a fine episode despite the discontinuities, with a climax that Babylon 5 fans are guaranteed to remember forever.