An expansion to Unreal, Return to Na Pali picks up not long after the main game's ending; Prisoner 849 is found by a human warship, the UMS Bodega Bay. Upon learning of the prisoner's identity, the military conscripts him or her into service, forcing the prisoner to return to Na Pali in order to locate the downed ship UMS Prometheus. There, the prisoner is to retrieve some secret weapons research. In return, he/she will receive a full pardon and transportation back to Earth. At least, this is what the prisoner is told; the real plan is to maintain the secrecy of the mission by killing the prisoner immediately after the information is secured.
Source: Wikipedia, "Unreal Mission Pack: Return to Na Pali," available under the CC-BY-SA License.