The episode fuses two completely unrelated story lines into a single episode. The "A-plot" involves the Enterprise flying through a strange cloud in space, unintentionally taking with it an energy-based life form that hops from person to person, and into the ship itself, before ultimately taking possession of Captain Picard. The "B-plot" has the ship ferrying delegates from two squabbling alien races (a stereotypical "snake race" and a stereotypical "dog race") to a peace conference.
The A-plot suffers from not quite settling on one thing it wants to be about. At first, it's a quasi-mystery about the alien energy consciousness drifting from person to person. What does it want? What can it do? Who will it possess? Will the crew locate and identify it?
Then, roughly a third of the way into the episode, the life form decides to jump into the ship instead. Suddenly, the episode is all about random ship malfunctions. Will the ship break down? Will the crew figure out the reason behind the malfunctions? Will they purge the computer?
But then, with roughly one-third of the episode left to go, the entity jumps into Picard and sets up permanent residence. Now the episode is about whether the captain is behaving irrationally. Can he be trusted? Is a mutiny in order? (In a later season, the writers would look back and realize the missed opportunity here, creating a new episode that was all about building up to a crew mutiny against a false Picard.)
What's really a strain in credibility is that the crew never really seems to connect these threads until Patrick Stewart -- as the alien -- gamely delivers a badly written expository speech at the climax of the episode. Until then, no one thinks to connect Picard's strange behavior to other crew members' memory loss during their periods of possession. No one thinks to connect the ship malfunctions to the recent pass through the mysterious cloud. The whole crew just gets a case of the dumb -- Wesley included, at least. His mother gets it the worst, though; Picard confesses to Beverly in one scene that he's possessed, yet she does nothing about it and leaves Riker to lament in the next scene that there's nothing they can do but go along with it.
The resolution of this story has the Picard/alien beam himself out into the cloud as pure energy, which the crew inside of three minutes miraculously reverses, beaming him back from nothingness. It's a ludicrous ending, but probably no more of an "ask" of the audience than the rest of the story. Still, you could almost call it the worst writing to that point on Star Trek: The Next Generation.
Or at least, you could if it weren't for the B-plot of this very same episode. Lame caricature aliens in lame full head masks are brought aboard the ship to snipe at each other while the Enterprise takes them to a peace conference. This is little more than an excuse for the crew to speechify. We get to hear about how our crew just doesn't understand this kind of racial hatred, and about how far humans have evolved beyond "enslaving animals" (the fish in the ready room would beg to differ) and fighting over "customs, God concepts, or even economic systems." Sure, these Roddenberry ideals are a nice sentiment, but they're off-putting when expressed in such a ham-fisted way.
The delegates are portrayed as so much at each others' throats that it's ridiculous to believe Starfleet would have wasted time ordering one of its ships to take them anywhere. These are supposedly peace ambassadors, but they spend the entire episode trying to kill each other, and one even apparently succeeds at the end of the episode. (In a moment that, most bizarrely of all, is played for comedy! Because racial genocide is just a barrel of laughs!)
Director Cliff Bole does manage to shepherd the cast through this nonsense, however. He worked on dozens more Star Trek episodes after this, for The Next Generation, Deep Space Nine, and Voyager -- and all probably because he did somehow get a couple good performance moments on film despite the awful script. Another decent element of the episode is the off-kilter score by Ron Jones, an effectively unsettling mix of tense strings with odd synthesizer phrases.
Other random observations:
- This marks the first appearance of the crew in dress uniforms. They really put the "dress" in dress uniforms, too.
- At one point, Dr. Crusher wears a silly helmet while performing a medical examination on Worf. Thankfully, it was never seen again.
- This episode was the first Star Trek appearance by actor Marc Alaimo, who later went on to play Gul Dukat on Deep Space Nine.
- There is a fantastically dry comic moment with Worf, when Dr. Crusher asks him about his memory blockout. His response? "I still don't remember having one."
- Colm Meaney is back as the still unnamed O'Brien, this time in a yellow uniform.
- Geordi at one point comments that they all might be in "beaucoup trouble." Like, gag me with a spoon, how gr-rody!
- The writers try to flesh out Troi's "I sense things" schtick with some actual science, having her conduct hypnosis on Worf and Crusher, and formally reporting the results to Picard. It's too bad this professional element of her character didn't stick a little better.
- The HD remastering team had a nightmare on their hands with this episode, having to re-animate all the arcs of alien electrical energy frame by frame to match the original.
Still, an interesting musical score and a fun Sherlock Holmes shout-out really isn't enough to pull this episode from the cellar of bad Star Trek episodes. I grade "Lonely Among Us" a D-. It should be watched only if you're watching them all.