A Romulan delegation arrives to study reports on the Dominion, a privilege granted in exchange for the use of a cloaking device aboard the Defiant. Meanwhile, O'Brien, at Quark's riding out a mild case of radiation poisoning from an accident, is suddenly transported to another part of the bar, where he sees himself having a conversation with Quark. He just as suddenly returns to where he was, then falls over in pain. Bashir blames the radiation and assures O'Brien that hallucinations are a normal side effect. But when O'Brien returns to the bar five hours later, he has the same conversation with Quark that he "hallucinated." Dax theorizes that O'Brien's exposure to radiation could have caused him to temporarily shift five hours forward in time. Then, O'Brien experiences another timeshift - into the middle of a brawl in Quark's between the Romulans and some Klingons.
Bashir examines O'Brien in the present and determines that the timeshifts pose a serious threat to his life. Five hours later, O'Brien returns to Quark's to wait for the brawl, and the Klingons soon arrive and exchange blows with the Romulans. O'Brien timeshifts again, and this time sees himself in a corridor. He watches as his future self opens a wall panel and is killed by a blast from a hidden phaser.
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"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.[1] The episode has an average rating of 4.4/5 on the official Star Trek website (as of 1 November 2007).[1]
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.
