"UnderWorld: Between the Worlds" served as a role-playing game adventure within the Living Force campaign setting. This adventure represented the third episode in the Between the Worlds trilogy, a series of adventures taking place during the campaign's initial year. The author of this adventure was Morrie Mullins.
The initial two adventures of the trilogy saw the player characters being employed by the criminal overlord Nirama with the task of penetrating the Cell, a dissident faction operating within his organization. In this particular adventure, the Cell secretly reaches out to the heroes, falsely identifying themselves as Nirama's operatives, and tasking them with the assassination of prominent figures within his organization. Their journey takes them to Rothe Gate, an asteroid dedicated to industrial activities. The player characters uncover the deception when Nirama makes his appearance on Rothe Gate, compelling them to determine how they will handle the circumstances.