After returning in a shuttlecraft from a bat'leth competition where he won first place, Worf arrives on the Enterprise to a surprise birthday party that mostly makes him cringe. (It's always fun watching the curmudgeonly Worf suffer through the social kindness of his shipmates, and Riker sets him up perfectly with a misdirection of denial.) But Worf experiences dizziness and disorientation and a shifting of details at the party. (A yellow cake becomes chocolate, and the captain, initially unable to attend, is suddenly present.) Is Worf hallucinating, or experiencing some other strange sci-fi episode? This is Star Trek: TNG, so what do you think?
"Parallels" is unadulterated Brannon Braga in the vein of "Cause and Effect," "Frame of Mind," and "Timescape," where strange sci-fi mysteries are afoot and the storytelling's effectiveness lies in its examination of details. These sort of stories are not particularly deep in their meaning or plausible in the strict (or, I suppose, any) sense of the word, but damn if they aren't entertaining in their exploration of shifting realities. It's not immediately clear to Worf (or us) exactly what's happening or why, but slowly we learn that Worf is shifting between numerous versions of an infinite number of possible realities. The theory goes that all things that are possible are actually happening in an infinite number of parallel universes, and "our" version of Worf is moving between them while maintaining all of his original memories.
This puts Worf in various universes where (1) he placed ninth in the bat'leth tournament instead of first; (2) he causes a tactical delay at a key moment that leads to an attack on the Enterprise; (3) he discovers that the Cardassians have reprogrammed a sensor array to spy on the Federation; (4) he is married to Troi; (5) he does not have a son named Alexander; (6) he is first officer on an Enterprise where Riker has been captain since Picard was killed in the Borg incident; (7) Geordi is dead; (8) Wesley Crusher is the tactical officer; (9) the Bajorans are powerful enemies; and (10) in perhaps the most subtle detail, Data has blue eyes. (I love how this detail goes completely without comment; it's a visual clue that demonstrates the infinite possibilities theory without underlining it.) Okay, sure, there should technically be versions of the universe that look nothing like the familiar surroundings anchored to a life on the Enterprise, but to that I say: Who cares?
A story like this can either be incomprehensible chaos or organized chaos. "Parallels" is a workable example of the latter. The story never becomes so zany as to be unworkable but instead slows down long enough to show that these various possibilities are real enough to mean something to the people involved. In particular, Worf's relationship with Troi makes him consider a possibility that he had never pondered, while at the same time he must confront a reality where his son never existed.
"Parallels" has a rather brilliant ending that is great in its audacity, where the quantum barriers between all these universes break down, leading space to fill up with thousands of Enterprises from other realities. (At one point, Wesley says he is receiving hails from 285,000 different Enterprises, clearly all confused.) In an inspired notion, one Enterprise is captained by a desperate and crazed Riker from a universe where the Borg have destroyed nearly the entire Federation; Riker has to open fire on this ship when it attacks. And there's something odd about one Enterprise having a viewscreen conversation with another. (And just who is the Worf on that Enterprise if "our" Worf is on this alternate Enterprise? Did they swap places?)
By sending Worf back to his correct Enterprise, the barriers will be sealed and everyone will be returned to their proper realities — though I was confused at why Troi was so saddened to "lose" Worf when he left; wouldn't "her" Worf be returned to her by this repair of the breakdown of reality? Or are there a finite number of quantum Worfs, and hers was somehow erased?
No matter — "Parallels" is great a high-concept story executed with high entertainment value and the right modulated tone. For those reluctant about the possibility of a Worf/Troi relationship being spawned from this — what can I say? In a universe where anything is possible, much stranger things have happened.