I don't know how to put this diplomatically: Star Control: Interbellum stunk. There's just no getting around it. The characterization was nonexistent, the metaphysics ludicrous and contradictory, they mischaracterize Ortogs (calling them tools of the Makers), it was extremely humanocentric (The Chmmr, the Orz, and the Arilou don't appear at all, and those are fairly major races to be ignoring...) and lots of it is just plugging Star Control III. W. T. Quick was also blatantly following the blueprint of the Monomyth in Joseph Cambell's The Hero of a Thousand Faces. In fact, this is how the good Captain is referred to.
You don't get much of a picture of space combat in Interbellum, but the scene in space is a great way of avoiding combat, playing two villains against the other.
If you want to run your Star Control game by playing the "War in Heaven" angle, then this will be helpful. Otherwise it's almost useless.
On Unzervalt, an Ortog is evolved to full sentience by the equipment in the Precursor caves. Jemmy Crost, the ortogherd that was in charge of this particular ortog, is suddenly targeted for extermination by the Tsing a Kra-- the Avatar of the Ur-Quan Great Hive. Commander Omega brings a team to Unzervalt to protect Crost.
Both the Tsing and Omega think that Crost is going to be the new Avatar of the Human Heart. Eventually Omega and the Tsing get into a confrontation in the transformation chamber, where Jemmy Crost is being transformed. The battle switches from between Omega and Tsing a Kra to the Heart and the Hive, respectively.
This goes on for awhile, then the transformed Crost orders them to stop. Crost is not the new avatar of the Human Heart, but rather the avatar of all gestalts. He effectively orders them to make up and join forces because something very bad is going to happen soon and they should all go to the core to try to fix it. (they don't mention the Eternal Ones, but that's the deal, and it's pretty transparent, too...) Omega and the Tsing cease being Avatars and rejoin the realm of the living.
Star Control 2/Interbellum: The Human Captain couldn't have become Omega immediately after destroying the Sa-Matra: It must have been after he left the hospital. The "Mark II" and the Galacticus are one and the same.
Interbellum/Star Control 3: The timeline in SCIII claims that the Galacticus was destroyed after Hyperspace stopped working: This obviously can't be true because the Captain is showing it to his grandchildren at the end of SCII. It was merely rendered inoperative. Also, the intro sequence must be regarded as erroneous, though it is likely that the Captain lied about his vision being after he destroyed the Sa-Matra. The Human Heart-- or perhaps Crost--was the one that imparted the vision of the Eternal Ones destroying the galaxy to him.
A few other points:
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