This is the fourth book in the Dragonsbane series. I read at least the first in this series a long time ago, but I'm fairly sure I never read the one just before this, and despite a section at the beginning summarizing what's gone before, I was rather confused about what was going on. If you seek to read this series, I recommend reading them in order, though finding all of them might be hard. Dragonstar is from 2002 and the others are a fair bit older than that; Dragonsbane I believe is from the early 90s.
This story features a bunch of bad guys, demons who are mainly fighting against each other but using the human world as a battlefield and playground as they go. The book looks at how society can't exist without a basic foundation of trust, as the demons possessing humans leave people not knowing who's really a demon. It also looks at the value of connections with others as some characters who start out only worrying about themselves gradually learn that others are important. The two main characters had a major falling out in the previous book and spend a lot of this one hoping they'll survive and be able to make up. A lot of compelling thematic material, but it didn't come together very well for me, perhaps partly because I spent the first half of the book trying to keep track of who was who. The main protagonist is an exceptionally competent individual, but we keep getting hit over the head with his folksy ordinariness. He speaks in a thick country-bumpkin patois that gets in the way of my appreciating him as a character -- despite being a world-class scholar who seems to be an expert on everything -- and even though we dwell quite a bit on how blind he is without his glasses, he still manages quite a lot of derring-do when he doesn't have them.
Oh, and somebody needs to tell the publisher that they need to choose a cover artist who understands that dragons are supposed to be beautiful.
There's a lot to like in this book, but I spent enough time being confused and frustrated as I read it that it never fully came together for me. 6 out of 10.
**** PLOT SUMMARY -- MASSIVE SPOILERS ****
It's more than a little muddled in my memory; I'm probably missing some things and I almost certainly have some events out of order.
We start the story with John Aversin, Dragonsbane, about to be burned at the stake for consorting with demons. The council that condemned him is mostly controlled by the demons that are taking over in Bel, but the charge is actually true. John had to do what he did, he saved the world doing it, and he's not in thrall of the Demon Queen. But he did have dealings with her. If he calls on her now, though, she will save him, but he will be in her power. He manages to hold to his convictions. After the pyre is lit, a dragon shows up, rescues him, and spirits him off to the ruins of Prokep. The dragon is Corvin, whom John rescued from the demons who had tracked him down where he was hiding as a scientist in another world, the subject of John's quest in the previous book; because John had saved him, Corvin owes him service. "Save a dragon, slave a dragon" is repeated so often through the story that it's almost a mantra. Corvin is obligated to save John's life but isn't very cooperative. John sneaks around on his own to learn the nature of the Maze here and to learn what he can about the Henge which seals the gates of hell where the demon lord Adromolech is trying to break out. Folcalor, Adromolech's traitorous lieutenant, is organizing an effort to use stolen souls and the power of the comet called the Dragonstar to break the henge. Corvin believes the Henge is invulnerable but John knows better. John also wants to save Gareth, the prince in Bel to whom he is friend and mentor, from the demons who are taking over. John learns the way through the maze and finally gets Corvin to take him back to Bel.
While this is happening, Jenny Waynest, John's wife who's become estranged -- she was possessed by a demon, she broke away but it left her emotionally scarred, she and John fought, and John walked out on her before going on the quest mentioned above, returning, and being set up to be burned -- is dying of a poisoned wound in the depths of the gnome caverns. Morkeleb the Dragonshadow -- earlier in the series he has progressed beyond being a normal gold-pursuing dragon to something mysterious -- has tried to rescue her and almost been trapped. But the gnome mage Miss Mab saves Jenny and she, too, tries to proceed to Bel to rescue Gareth. John and Jenny meet and work on saving Gareth, but Gareth is clinging to the delusion that the child his wife was pregnant with when she was killed and possessed by a demon is still his human child, though he should know better that it will be born as a demon. They rescue the kid but Gareth is too slow to move and is taken a prisoner.
Somewhere in here, the demons make a preliminary attack on the Henge, almost taking Corvin by poisoning the air with gold dust (powerfully intoxicating to dragons), but John manages to wake him in time. Corvin, at least, becomes convinced that there is real danger, but he just wants to flee to the Skerries of Light. Also, somewhere in here, Jenny has gone to the ruins of Ernine and recovered a catch-bottle which will trap the Demon Queen. Jenny manages to catch her in the bottle but discovers that when she does, she is also trapped in the spell. The only way she can escape is to free the Demon Queen, and the Demon Queen convinces her that Jenny has to let her go so that she can save Gareth.
In the process of rescuing Gareth, John collects the sword that he got from the world Corvin was hiding in. The sword has the power to actually slay demons; normal weapons only kill the bodies they have taken over. The possessed king is killed by a horrible monster, and John kills the monster and some of the demons, including the one that had possessed Jenny.
John and Jenny manage to rally the dragons to defend the Henge against the attack. They trap the demons inside a new henge, powered by the ether (which seems to be electricity) from the world Corvin was hiding in. They have arranged to re-key the catch bottle to Adromolech (after prying his name from Caradoc, a wizard who had lost his body in an earlier demonic possession, for whom John built a robot body which Caradoc didn't find satisfactory) and given it to Folcalor. Folcalor and Adromolech trap each other, and many of the other demons are trapped inside the new henge and eaten by the Shining Things, beings who really don't like demons (and, like the sword, have the power to truly kill them) which John had learned about on his quest through hell.
The demons having been put down again, Gareth is installed on the throne and everyone gets ready to peacefully rebuild the kingdom. Looking back, John concludes that a lot of the events as they transpired were actually the Demon Queen's plot; he believes she wanted to put the other demons down, not so that she could take over the mortal world, but so that she could just reign in her own hell in peace. (The Demon Queen is a very ambiguous character; sometimes she appears to be a friend and an ally of the good guys, but she's still a demon and at best not to be trusted.) Morkeleb is still trying to figure out his new role as a Dragonshadow, and he plans another quest with John and Jenny, presumably in another book that Hambly might write someday if she goes back to writing fantasy.