From publisher blurb:
Hypergates of the Lost Empire is an adventure scenario designed for Overlords of Dimension-25, an OSR-style science fiction roleplaying game inspired by RPGs from the early 90s based on the pulp-era exploits of a man transported to the 25th century.
The rules are based upon and similar to those of the world’s most popular fantasy roleplaying game. Before playing this scenario the gamemaster and players should become familiar with the Overlords of Dimension-25 game rules or those of its inspiration.
This adventure scenario is a sequel to City at the Edge of the Universe, but can be played as a stand-alone story.
Hypergates of the Lost Empire can also be used with other OSR-style science fiction roleplaying games with little to no modification. A hit point is still a hit point and an armor class is still an armor class.
This adventure scenario is designed for 4-6 player characters of 3rd to 5th level. The player characters should include at least one character displaced from Dimension-Prime - that is, our modern dimension - and one medic. If there are none, the gamemaster should add one or more support Non-Player Characters (NPC) - specifically someone displaced from Dimension-Prime and a medic equipped with a bioscanner, a trauma kit, and an auto-surgeon.
This adventure scenario assumes that player characters are either agents of the Earth Resistance or freelance operatives hired by them. If the characters represent a rival faction, such as the ARES Consortium, Solar Syndicate, UEA, Lunar Union, or Trade Confederation, the mission is essentially the same, only the details change.