The U.S.S. Enterprise learns of the disappearance of a medical transport ship, the U.S.S. Fleming, which vanished in the Hekaras Corridor, the only safe route through an area of space filled with tetryon particles, which pose a navigation hazard to warp-driven vessels. When they discover that a Ferengi ship was also spotted in the area, Beverly Crusher suggests the Ferengi may have hijacked the Fleming to steal its supply of valuable bio-mimetic gel. All agree that this is a possibility and set course for the area. The Enterprise locates the Ferengi ship, and the crew is surprised to discover the ship's field coils have been overloaded and it is operating at very low power. The Ferengi vessel does not respond to the Enterprise's hails, but suddenly regains power and fires on the starship.
The Enterprise returns fire and disables the Ferengi vessel's weapons system, after which Picard contacts the Ferengi commander, DaiMon Prak. Prak meets with Picard and Riker and tells them that his ship encountered what appeared to be a Federation signal buoy, but it suddenly emitted a verteron pulse that caused it to lose power. While Prak admits to having seen the Fleming, he refuses to help the Enterprise locate it unless their engineers help him repair his vessel. This is agreed to, and the Enterprise soon sets course after the Fleming, tracing it to a debris field. They enter the field and encounter a small object that emits a verteron pulse. Suddenly, their subspace systems are disabled — just like on the Ferengi ship — then two aliens board the Enterprise uninvited.
The Hekaran brother and sister, Rabal and Serova, claim that according to their research, the use of warp fields in the area is destroying their planet and will soon render it uninhabitable. They have been disabling offending ships in hopes of forcing Starfleet to investigate. They explain to Geordi that the use of warp drive is so harmful to their system that they are willing to give it up — a move that will effectively isolate their planet from the rest of the Federation. Data finds that their theory could be valid and asks Picard to summon the Science Council for a more thorough investigation. However, this does not satisfy Serova, who dismisses it as a stalling tactic. She suddenly takes off in her ship and creates a warp breach, sacrificing her life to prove her theory by creating a dangerous rift in space.
Data learns that the Fleming is trapped in the rift, which emits high-energy distortion waves that rock the Enterprise. Picard orders Data, Geordi and Rabal to find a way to get the Fleming out without using warp drive, and Data suggests they coast into the rift after initiating one brief warp pulse. The crew puts the plan into effect, and Geordi, realizing he has been unwilling to consider the dangers of a technology he is so close to, apologizes to Rabal for his loss. They then coast into the rift as planned, but the Fleming activates its warp drive and makes the rift even larger, severely damaging their ship in the process.
Left without enough momentum to leave the rift, Geordi suggests the Enterprise "ride" a distortion wave out after the evacuation of the Fleming is complete. After several aborted attempts, he manages to "catch" a wave and the Enterprise escapes the rift. Once things get back to normal, the crew meets with Rabal, who shows them the possible effects of continuing warp damage. Based on the Enterprise's reports, the Federation Council issues a new directive limiting all Federation vessels to a speed of warp five, except in extreme emergency. Later, Picard sadly tells Geordi how, by exploring the universe he loves, he may have inadvertently been destroying it. Geordi is reassuring, reminding the Captain that now that they are aware, they can work to help the universe rather than harm it.