Looking for title and author: fantasy, shapeshifting thief, sorceress

Question

Pretty sure this book was fantasy, rather than sci-fi. Probably late 70s early 80s. I remember:

The world is made up of separate chunks, islands floating in space, each following a specific path that is charted and regular (there are timetables written about the movement and paths of each island). A thief cases a house to steal an artifact, a crystal crescent. The crescent is resting on a cushion on a mantel, in a room where the floor is specially made so that if you step in the wrong place, the floor shrieks like a riven vampire. The thief returns at night, navigates the floor, discovers that the crescent is protected by a glow (spell), figures out that the spell doesn't affect the silk cushion the crescent is sitting on, so makes a loop out of a piece of silk from his own clothes, and leaves (something) behind on the cushion, to give the spell something to protect. To leave the building, he goes to a pantry/closet with a window, and has to dislocate his shoulder to fit. I want to say that he can shapeshift into a bear, but I can't remember how that fits in anywhere. Further on, he meets a sorceress, who wears a ring made out of crystal on a particular finger to show her rank.

And that's what I remember. I want to say the author is female, but I can't remember the name of the author or the book, and the copy I read was missing its front cover so I have no idea of the cover art. Please help!

Answer 1

I love this book too! The Shattered World by Michael Reaves. Without a doubt.

A thousand years ago, the world was broken in a great cataclysm; now people live on the fragments, flying between them in ships made of the skin & bone of dragons. The book follows the interweaving stories of a thief, a couple of wizards, and various others as events are set in motion that will take them on perilous journeys to the far reaches of the world with far-reaching consequences.

Matching details from my memory:

• Floating land masses in breathable atmosphere
• Werebear/lycanthrope/shape changer thief protagonist
• Sexy deadly woman wizard antagonist
• Botched jewel heist

But honestly, you must not have gotten too deep into the book because the best parts you don't mention, nor will I because of spoilers. The jewel heist is just the beginning of events that entangle the thief in a global plot.

And it was 1985, not the 70s!