This book is the first of trilogy set in that magical time of medieval anachronistic romance when knights charged about in the Dark Ages in a manner more befitting several centuries later. Vance has plonked several legendary realms (for example Ys, Avalon, and Lyonesse) on an archipelago in the Atlantic, the Elder Isles, which sinks without trace (or record) centuries later.
The book has a low key start in the palace of Casimir the King of Lyonesse. However, it quickly becomes clear that the garden is merely the starting point of the story and it quickly expands to include other warring kingdoms, mages, and magical creatures.
Vance's world is a brutal one. People die a lot and sometimes randomly. Bad things happen. There is one brutal twist which really shakes up the story. However, the omnipresent narration distances the reader from events to some degree so it never tips into the realm of grimdark. The mood is often more akin to that of a classical fairy tale.
The world building is detailed but in some ways random to create kind of a 'springy' effect.
There are a couple distinct threads in this story most of which branch out from Suldrun. The mages' subplot on the other hand starts out separate but eventually intersects with the others. However, perhaps thanks to an embargo on mages on intervening in political matters, it feels as their struggle and the kings' rivalry often just glance off each other. The book is full of digressions and tangents, but the imaginative scope of the book cannot be denied.
There are loose threads at the end but you would expect that given it was obviously envisaged as part of a trilogy. One thing I did have a problem with was the epilogue which I suppose was meant to wet the reader's appetite for the next volume but, to me, felt very much like somebody just hit the fast forward button, speeding events by without context.