It's kind of like a holodeck episode, minus the holodeck.
The Enterprise finds a strange building on a strange planet. While investigating, they find the remains of a long-dead NASA astronaut - Also, the away team becomes trapped in a Casino-like atmosphere as described in a book that the astronaut happened to have on him. It appears that the casino was constructed by misguided aliens who wanted to give the astronaut a nice home after accidentally killing every one else on his crew. To escape, the away team must analyse the novel and convince the artificial patrons that they are the "foreign investigators" described therein. Luckily, the novel's fairly predictable.
Unfortunately for this episode, the back story sounds more interesting. We don't actually get to meet any aliens, just stereotypical casino lurkers. Now, the premise of the aliens basing their construction off of a book, and the away team being trapped therein, that part is fine. That's the interesting part, the part that screams Twilight Zone. But a casino? Eh. Didn't we have a mobster holodeck episode back in Season One? Also also in the original series? For some reason casinos and mobsters are linked in my mind, and Sherlock Holmes isn't all that tangential. So, for me, this episode feels like the revolving door that poor Riker tries to leave out of. Man, I hate revolving doors.
You know what might have been cool? If the astronaut were still alive! That might have added some urgency to the situation, even if the Enterprise wasn't able to save him in the end. It might have introduced more screaming and horrified looks. Screaming is always good!