"Clues" is one of those bottle shows that works better the first time you see it. It's intriguing when you don't know what's going to happen. But it loses something the next time through. As mysteries go, "Clues" holds the attention reasonably for an hour. The questions are: What happened, and do we dare try to repeat history when we have no memory of the consequences?
As they approach a planet, the Enterprise crew is unexpectedly rendered unconscious. Upon awakening, Data, unaffected, says the crew has been out for 30 seconds. Gradually, however, clues are discovered that Data is probably lying, that the crew was unconscious for much longer, and that something serious happened that no one can remember.
What works best about this story is its pace. It's a slow burn that gradually reveals peculiar clues hinting at an inevitable truth: Data is covering something up. The evidence — from Crusher's botany experiment to Worf's broken wrist to Troi's freak-out in the mirror — all paints an odd picture surrounding the original mystery of the planet the crew never reached before blacking out. My favorite dialog scene is between Picard and Data, where a frustrated Picard grills Data on the facts and Data simply says that he cannot answer. (When Data stonewalls, he's never anything but calm, polite, and matter-of-fact; he can't answer simply because ... well, he can't.)
What doesn't quite work is the explanation for this whole charade. A group of isolationist aliens wiped the crew's memory because they didn't want to be found. Except Data's memory could not be wiped, so Picard swore Data to secrecy rather than allowing the aliens to destroy the Enterprise. But it didn't work and now we need a second chance, this time leaving no clues. I'm not sure how you leave no clues on a ship with 1,000 people.
The episode, which opened with Picard on the holodeck trying to solve a Dixon Hill murder, does not take the subtle road regarding its message, which is that we cannot resist a good mystery. One wonders if Picard's holodeck games and his speech at the end are both necessary. Show, don't tell.