Star Trek: Voyager, Series 6, Episode 7.
First broadcast on Wednesday 10 November 1999. Stardate: 53167.9.

This week, the crew of the USS Voyager awaken an ancient evil and unleash it upon the Delta Quadrant: the Vaadwaur, a phantom army that appears out of thin air, destroys entire colonies, and vanishes in the blink of an eye — but whose soldiers’ physiognomy is such that few men can find them afterwards.