Sapphire Blue picks up where Ruby Red left off--Gwen and her time traveling partner Gideon are making regular trips back in time to meet with Count Saint Germain and others to work out the mystery of why they are the last time travelers and why their distant cousins Lucy and Paul have stolen the other chronograph to keep the Circle from closing. Gwen is seen as a poor replacement for her cousin Charlotte and Gideon keeps giving her mixed signals. Despite all this, Gwen begins investigating on her own, running into a young version of her beloved grandfather who decides to help her. Danger lurks; Gwen suffers humiliation; people aren't who they seem to be. This middle book sets the stage nicely for the final book, Emerald Green.
I love Gwen because she's such a real character who puts up with a lot of nonsense from those who should be most supportive. She's tough and she doesn't play by the rules, but her weakness is obviously the hard to read Gideon. He was quite irritating throughout this book, never giving clear vibes as to his intentions and what he knows about the Circle. The real surprise for me was that I liked the appearance of Xemerius, a ghost demon only seen by Gwen; usually these types of characters make me lose interest in a story because they seem silly, but Xemerius is actually funny and helpful in ways almost none of the humans are. In general, I'm pretty irritated by the secrecy and arrogance of the adults and Gideon, and will be glad to see if Gwen can take them all down a few pegs as she solves the mystery.
Sometimes a middle book in a series suffers from lack of action and the addition of non-essential information, but Sapphire Blue seems to have transcended those issues and gives a good story that furthers the overall plot well. I love Gwen and can't wait to see where all this time traveling ends up...but it looks like I've got a year to wait until the final book comes out.