Rhapsody in Black, by Brian M. Stableford

This is the second Hooded Swan book I've read (the first was #5, The Fenris Device) so I know that Grainger is a star-pilot on the Hooded Swan, and he has an alien consciousness that's stowed away in his mind. Grainger calls the alien the wind, and doesn't much care for him. The wind give commentary and unwanted advice, and claims that he can't take over Grainger's body against his will—but Grainger isn't so sure.

Rhapsody
Grainger and crew head to the planet Rhapsody, whose surface is so poorly suited to life that the local cult lives underground in tunnels and caves. The local cult? They're an ascetic religious order called the Church of the Exclusive Reward. Rhapsody, being such a poor world, is perfectly suitable to them. But someone has discovered something exceedingly valuable on Rhapsody, and Grainger's boss Charlot wants in on it.

Kidnapped by pirates is good
Well, not kidnapped by pirates. Rather, imprisoned by the cult. As soon as the Hooded Swan lands on Rhapsody, the whole crew is thrown into prison. Grainger quickly busts out, but on a planet where the only inhabited or inhabitable place is in the caves and tunnels beneath the surface, well, there aren't many places to go. He eventually finds his way to a remote cave and falls in with a warren of outcasts. These poor folks have transgressed the laws of the Church of the Exclusive Reward and have been excommunicated. The Church takes this excommunication seriously: nobody is even allowed to acknowledge their existence. Grainger explains what he knows—something valuable has been found on Rhapsody—and the outcasts decide this is their ticket off-planet. They'll seize whatever this valuable thing is, sell it, and go make a decent life elsewhere.

Invisible rebels
Remember the part about how good Churchmen aren't even supposed to acknowledge the existence of the outcasts? Well, that helps make it easier (a little) for the outcasts to seize the grotto where this treasure has been found. It makes it much harder, however, to negotiate for a way out. The rebels (and Grainger) have seized the grotto and the treasure, and have several hostages to boot, but they can't negotiate because nobody will acknowedge their existence.

Well, except for Grainger. Grainger is merely an off-worlder, not an outcast, so he becomes the spokesman and go-between. The negotiations are nearly derailed when it becomes clear that the rebel leader, Bayon, is more interested in going out in a blaze of glory than in achieving a mutually-beneficial outcome. Bayon meets his demise but the rest survive.

The treasure?
The treasure turns out to be a unique form of life discovered in this a grotto: a life form that feeds on specific form of copper that most of the galaxy relies on for their building material. This creature is a fantastic weapon that any major power would want in their arsenal. As Grainger puts it, "it eats cities." In the end, though, there's a fatal flaw that may make the weapon useless—it's allergic to humans and dies if touched.

My take
I enjoyed this one. It's not amazing, but it held my interest. Thumbs up.