The Enterprise makes a diversion to Omicron Theta, a deserted human colony where Commander Data was first discovered by Starfleet personnel. While exploring the laboratory of Data's creator, Dr Noonien Soong, the away team discover an identical android. When the new android, named Lore, is assembled, it turns out he may know more about the whereabouts of the missing colonists that he lets on.
The evil twin storyline is one that comes up again and again in science fiction and fantasy. It's such a well-worn trope that it's not really a surprise that The Next Generation would use it. Brent Spiner plays both Data and Lore, and it should be said first and foremost he does a stunning job of it. Lore is a much more complex, emotional character: funny, cruel, vindictive and arrogant. He's a great villain, and it's not a surprise that he returns to the series in two more episodes down the line. Sadly while Lore is great, the episode surrounding him is not as successful.
There are enormous gaps in logic in this episode, as if entire scenes were removed. Why is Lore evil? What is the Crystalline Entity that destroyed the Omicron Theta colony? How did he contact it in the first place? Why did he want the colonists to die? Why does it cooperate with him? Why do the Enterprise crew trust him? Why don't they trust Wesley, who gets rudely shouted down every time he points out that Lore has put on Data's uniform to impersonate the officer? This is an episode with action and suspense, but no motivations. The result is a visually adept but hollow exercise.
Perhaps the biggest problem with the story is that in order to work it requires the Enterprise's bridge crew to be purposefully stupid. There's a writing term: the 'idiot ball'. Basically in a poor storyline, a character has to behave in an uncharacteristic or stupid manner for the plot to work. The writer has tossed that character the metaphorical idiot ball, and while they hold it they suddenly become remarkably foolish. This episode is full of idiot balls, flying so thick and fast it's like a paintball match. It even retroactively throws idiot balls into the backstory: did the crew of the USS Tripoli really visit Omicron Theta, find a deactivated android and an entire human colony missing, and then simply leave? It takes La Forge about two minutes to find Dr Soong's laboratory on his own. Surely a starship investigating several hundred missing humans would at least do a cursory scan or two before leaving? The whole plot defies belief. It makes no sense. It treats everyone like a fool: the characters, and particularly we the audience.
So we're at the 12 episode mark, and The Next Generation has managed four watchable episodes. We're back to a score of 33% - I may never be mean to Babylon 5's first season again.