Dr. Pulaski, ever the Bones clone looking for a Bones/Spock dynamic, challenges Data to an exercise in human improvisation: solve a Sherlock Holmes-style mystery that was not covered in the original source material. Is he capable of human insight beyond the Boolean logic of computer hardware? Geordi instructs the holodeck computer to create an original mystery with an adversary capable of defeating Data in a duel of wits.
Again we venture into the world of the period costume piece, a la first season's "The Big Goodbye," and like that episode, this one takes its time getting up to speed. I could've done with a little bit less of the Sherlock Holmes material and more of the sci-fi stuff. I think the story also makes a mountain of a molehill where Geordi's "slip of the tongue" is concerned. (Who cares if he instructed the computer to create an adversary that could "beat Data" as opposed to the fictional Holmes? The computer's sentient capability is the issue, not whether misspeaking one word can, or even does, cause it.)
Fortunately, the destination of "Elementary, Dear Data" is well worth the wait, and builds on the one moment of inspiration that "The Big Goodbye" had going for it: the idea that a computer program could become self-aware and grow beyond what it was designed to do. In this case, the intellect of Professor Moriarty (Daniel Davis) grows beyond the holodeck's parameters and is able to witness and participate in events outside its programming. The scene where he calls for the arch is an intriguing moment: We find ourselves asking, what does this mean? When he eventually is able to tie into the Enterprise's computer system and start shaking the ship, he gets Picard's attention.
What I like about this episode is its TNG sensibility. I could see Star Trek today using this as a gimmick solely for an action plot, but in 1988, the story exhibits a genuine curiosity about who Moriarty is now that he knows he's not part of the world he was created for. Picard and Moriarty have an exchange of dialog that's also an exchange of ideas, and they reach a peaceful resolution. It says a lot that Moriarty is willing to put his fate entirely in the hands of someone who could simply order his destruction in the interests of safety. But TNG was really about seeking out new forms of life, and this story highlights the series practicing what it preaches.