To solidify its power, a planet-eater tracks down the only thing which could threaten it, the "matrix of power", a device passed down from the leaders of a race of alien robots.
This was a deeply-moving movie for me as a child, though this impression was only possible because I grew up watching the original series. Re-watching this as an adult, it didn't have anywhere near that impact.
Though I do still like it, I don't know that I can recommend it, not just because it looks "old", but because it requires so much context from the series. I think for the young these days this would look like a crappy old cartoon with decent, but old, rock music.