The Nyrians were a race of humanoids who inhabited the Delta Quadrant. Although externally identical to Humans, they were highly sensitive to cold and light and were uncomfortable in humid environments as well.
In 2373, the Nyrians attempted to take control of the USS Voyager using their translocator. The Nyrians gradually exchanged themselves for Voyager crewmembers at the rate of one every 9 minutes and 20 seconds, and put the Voyager crew on board their biosphere vessel.
At first the Nyrians made it appear as if they did not know what was going on; they acted just as confused as the Voyager crew upon arrival. By the time the crew realized what was occurring (with the exception of Captain Janeway who had been suspicious all along) the Nyrians outnumbered the crew and took control of the ship.
Janeway and Tuvok eventually gained control of the translocater device, and translocated two senior Nyrians into one of the coldest environments on the habitat ship. They were then able to convince the Nyrians to surrender and set about freeing the thousands of other prisoners the Nyrians had taken. (VOY: "Displaced")