A starship emerges from a mysterious void. It's on a collision course with the Enterprise, which is dead in space because of power disruption. The crew has only a few seconds to make a decision on how to avoid the collision. They try to deflect the other ship with a tractor beam, but the ship hits one of the Enterprise's warp nacelles. A cascading catastrophe results in a core breach that destroys the ship.
And then, after the commercial break, repeat.
"Cause and Effect" is like the Groundhog Day of Star Trek (it aired a year before Groundhog Day itself was released), and its one of my favorite TNG sci-fi mysteries. It's a time-loop story featuring subtle nuance in its details, intriguing clues, and foreboding atmosphere. It utilizes the characters sensibly. And it also has the Enterprise blowing up four times. How awesome is that? (Sure, the Enterprise exploding should've been more spectacular, but with 1992 visual effects whaddaya gonna do?)
This is the sort of lightning-in-a-bottle sci-fi high concept that Brannon Braga would try to recapture again and again on TNG, Voyager, and Enterprise. It would eventually become his reputation (often not in a good way), though I think that reputation may be somewhat unfair. It's reminiscent of second season's "Time Squared" in that it depicts a time loop, but it goes one step further in showing the time loop as played out over multiple iterations, where the crew becomes slightly more aware of the loop as the story progresses.
Lots of nice details pull together to create some memorable atmosphere. The poker game, for example, begins as innocuous off-hours recreation, but by the end, as the players are able to predict the cards, it becomes downright eerie. (Data has the line of the night regarding these predictions: "This is highly improbable.") Geordi shows up in sickbay, and Crusher has deja vu. People throughout the ship hear strange whispers at night; what might they be?
And in my favorite little detail, Crusher cannot seem to escape the fate of breaking the glass in her quarters, even when she has a premonition that she's going to break it and tries to take action to avoid it. This detail hints at the notion that perhaps the Enterprise itself cannot escape the fate of its own destruction (though obviously it ultimately will).
Scratch that — my favorite detail is that once the crew discovers what is happening and that they can send a very short message (no more than a single word) from one iteration of the loop to the next in order to warn themselves of the disaster, Data sends the number "3" to his future self and then the 3's show up all over the ship in places he subconsciously planted them — including stacked in the poker hand he deals. Neat. (The 3 refers to the rank insignia on Riker's collar, allowing Data to realize Riker's suggested course of action may be the correct one to avoid the crash.) "Cause and Effect" has no deep significance or important message. It's simply an ingeniously conceived, well executed sci-fi yarn, where the truth is in the details.