They come across a strange planet in the far reaches of space. It's not on any of the maps or star charts. They almost fly right into it. Their scans can just barely penetrate the atmosphere, all they detect is a massive amount of biological matter on or near the planet.
They may choose to ignore it or might explore this strange planet. Upon entering the atmosphere they're met with a nightmarish scene. Writhing black tentacles cover the entire surface like some sort of hideous forest. They then detect a massive energy signature. The energy is coming from a massive temple built upon the service, in the temple is a cult of humans complete with black robes, chanting, etc. Upon further investigation they discover the cult is actually worshiping the planet, the planet is just one huge organism. The cult believes that it is a god and wish to use it to 'devour' other planets.
Just an idea, just throwing it out there.