This not the book I'd start with if you're new to Anne Bishop or her Dark Jewels series. I'd recommend reading at least the opening trilogy first of Daughter of the Blood, Heir to the Shadows and Queen of the Darkness, despite the fact this novel precedes them chronologically (set a few centuries before) and could stand alone. I think however that earlier written trilogy is the stronger introduction to the Dark Jewels series.
The story in The Invisible Ring is alluded to briefly towards the end of Queen of the Darkness, and if you've read that book you might recognize the reference. Although I didn't find this story as striking as the original trilogy--it's more of a standard romance--Bishop does have the ability to make you care about her characters, particularly Jared and The Gray Lady, and draw you into their world. I loved the device alluded to in the title of The Invisible Ring, which has the perfect pay off in the last lines of the book. The novels The Shadow Queen and Shalador's Lady, chronologically set after the original trilogy, are more or less sequels to The Invisible Ring, since that novels acts as a backdrop to them--I'd recommend both, particularly if you enjoy this book.