After Worf loses a photon torpedo. Picard takes Data with him on a three-day shuttle jaunt to find it. I realize so far that probably sounds like a joke, but it’s accurate.
They return to find the Enterprise-D adrift, and the corridors filled with animal noises. (I was listening with headphones, and the audio effects were great.)
Picard for some reason decides to stop by Troi’s quarters, where he finds the counselor is now an amphibian. Lurking in the ready room, Riker is a grunting, hairy-knuckled primate; Worf is a spiky, venom-spitting predator, and Spot the cat is a lizard (with a pink collar around its neck).
I was not impressed when I started watching this episode midway through 30 years ago. I didn’t hate rewatching it as much as I thought I would. It was definitely cringey, but it was also kind of fun.
The episode (directed by Gates McFadden, who portrays Dr. Crusher) starts in a busy sickbay, with comic vignettes featuring Lt. Barclay’s latest self-diagnosed imagined illness; Riker with thorns in his back because he was getting amorous with a date in the arboretum; Data with his pregnant cat; and the recently promoted Lt. Ogawa revealing that she, too, is expecting.
Crusher does Medical Stuff to Barclay, activating a dormant gene that should have been fighting off a mild alien flu. As she does this, she casually infodumps a brief genetics lecture, which makes it just a bit easier for us to accept the silly “de-evolving into more primitive life forms” premise.
The transition happens slowly. Worf is still brooding about losing his torpedo, and snaps at Riker, who orders him to take a break. He has a plate full of tentacles and random meat, and he’s gnawing and burping when Troi joins him in Ten Forward. Later, he rips up his bed to make a nest on the ground, and becomes more bestial. Riker gets sluggish and forgetful; Troi gets more thirsty and, I guess, more amphibious.
As Data works on the science necessary to reverse the de-evolution (Spot’s kittens and Ogawa’s baby lead to the solution), Picard must distract and evade the creature Worf has de-evolved into.
The creature effects were pretty good for TV, though I wasn’t impressed by Troi’s amphibian makeup.
We learn from dialogue that 1000+ people on the Enterprise-D have de-evolved in to various creatures, many of them gathered in the arboretum — but we never see a creature-infested arboretum, and the story doesn’t cover what those primitive beasties ate during the 3 days Picard and Data were away. Presumably some of them ate each other, but the final act seems to suggest everything returned to normal after Data spread his airborne gene-fixing cure through the ship.
On my rewatch I was impressed by the stray torpedo special effects, and shots where the shuttlecraft makes a shadow that passes over the saucer section, and when the shuttle changes its orientation to line up with the drifting Enterprise. They looked so clear. Knowing these were filmed with models 30 years ago, not with CGI, I always enjoy seeing fresh space FX shots.