Classic Star Trek episode from the original series second se …
"Cause and Effect" is the 18th episode in the 5th season of Star Trek: The Next Generation. It features guest star Kelsey Grammer and was directed by Jonathan Frakes from a script by Brannon Braga. It originally aired as Episode 518 on 23 March 1992 (Stardate 45652.1).
According to an opinion survey website, "Cause and Effect" has been voted one of the top ten episodes of the series. The episode has an average rating of 4.4/5 on the official Star Trek website (as of 1 November 2007).
The Enterprise-D is shown to be stuck in a time loop, with events culminating in the destruction of the ship as a result of a collision with another Starfleet vessel that emerges from a space-time distortion. As each loop proceeds, the crew members, though unaware they are in the loop, have the feeling of déjà vu; Dr. Beverly Crusher begins to hear numerous conversations before going to bed, and during one cycle, manages to record the voices on a tricorder. Analysis reveals that the voices are Enterprise crewmembers seconds before the destruction of the ship. The crew discovers the time loop is caused by tachyon distortions near the space-time anomaly, and program Data to send a short message to his counterpart in the next iteration to take action on. Data sends the signal moments before the ship is destroyed again.