Star Trek: Voyager: Dark Matters #1: Cloak and Dagger

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....
CLOAK AND DAGGER

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!