Star Trek: Voyager: Dark Matters Series by Christie Golden

It is a scientific truth that the structure of the universe depends on the amount of "dark matter" contained in the cosmos. When sinister forces threaten to tamper with the very nature of reality, Captain Janeway and the crew of the U.S.S. Voyager must risk everything to restore the universal balance....Years ago, near the beginning of its long journey, Voyager made contact with a brilliant Romulan scientist whose present was Voyager 's past... moreIt is a scientific truth that the structure of the universe depends on the amount of "dark matter" contained in the cosmos. When sinister forces threaten to tamper with the very nature of reality, Captain Janeway and the crew of the U.S.S. Voyager must risk everything to restore the universal balance....Years ago, near the beginning of its long journey, Voyager made contact with a brilliant Romulan scientist whose present was Voyager 's past. Now Telek R'Mor communicates with Janeway again -- to warn her of a dire plot to capture Voyager and turn its "future" technology against the Federation of yesterday. But more than just the timeline is at stake. Voyager itself may be carrying a menace deadly to all creation! less

Scientific theory holds that ninety percent of all matter in the universe is "dark matter," unable to be detected by ordinary means. The gravitational force of that mysterious material ensures the continuance of all reality, but now a cosmic conspiracy plans to use excess dark matter to bring about the death of the universe... moreScientific theory holds that ninety percent of all matter in the universe is "dark matter," unable to be detected by ordinary means. The gravitational force of that mysterious material ensures the continuance of all reality, but now a cosmic conspiracy plans to use excess dark matter to bring about the death of the universe. While Chakotay and Paris are lost in a mysterious shadow dimension, Captain Janeway and the remainder of her crew struggle to contain the deadly dark matter wreaking havoc on the ship -- and deep in space. But malevolent forces are working against the Starship Voyager™, and they have seduced the Romulan Empire to their cause! less

The trilogy draws to a conclusion as Voyager races against time to gather a deadly contaminant. Whose side are the Romulans on? Where is the missing piece? And what surprising figure from Voyager's past holds the key to the fate of the universe?