Adventure Gateway 2: Homeworld 1

A few years after your adventures in Frederik Pohl's Gateway, a massive artifact warps into our solar system. Nobody is sure what it is, or where it came from, but there's specuulation it could be a ship for the Heechees. A sect is convinced it's actually a vessel from the Assassins, whom they want to guide towards our planet in orfder for humanity to be cleansed.

You are asked to help out with some consultancy work, but while you are at the military base, it comes under attack from the sect, and your only escape is to board the ship headed for the artifact.

The game is divided into 4 major parts, with the first one taking place on earth, the second one on the artifact, the third one on a distant planet, and the 4th part in the Heechee world.