Ensign Lang was an operations division Starfleet officer assigned to security aboard the USS Voyager, under the command of Captain Kathryn Janeway. She was one of the crewmembers who survived the transport to the Delta Quadrant in 2371.
Later that year, Lang was acting as chief of security after a majority of the Voyager crew had been translocated to the Nyrian biosphere vessel. She was later left in command of the bridge. While in command of the bridge, she coordinated with two of the remaining twelve crewmembers and communicated that they had to prevent the Nyrians from capturing the bridge. Seconds later, a few Nyrians stormed the bridge and Lang stunned two of them, before she was, herself, stunned. She was subsequently transported to the biosphere vessel, where she was imprisoned with the rest of the crew. (VOY: "Displaced")
In 2377, she was affected by radiation when a mine exploded near Voyager's hull. She and the rest of the crew left in escape pods and were rescued by the Quarren, and treated for their radiation burns. However, what the crew didn't know was that the Quarren intended to alter their memories, and make them join their working class.
When Commander Chakotay infiltrated Quarra to find the crew the first time he entered the main power distribution plant, he passed Lang working there. Later, her memories were reintegrated, and she returned to life on Voyager. (VOY: "Workforce")