I'd always have to say The Lymond Chronicles. It is hard for me to think of them as anything but a whole. If I did though, it would be The Ringed Castle. It was the first book of the series that I read, hooked me into the series, and I lived through anxious years before Checkmate was published. I was enchanted by the "Languish locked in L" part long before I knew that it was favored by so many others. My Elizabeth icon has a quote from The Ringed Castle.

What is the difference between a summer spread and a quilt?