"Sapphire Blue" ended with our heroine heartbroken, believing that her love Gideon had been manipulating her all along. 
 And "Emerald Green," the final volume of the Gem Trilogy, picks up immediately after that. Despite a slightly rough beginning (yes, you got used. Get over it!), Kerstin Gier's smooth, colorful prose brings a light touch and turbulent romance to the time-traveling heroine, neatly tying off the important plot threads and adding in a twist or two. 
 Devastated by Gideon's betrayal ("It feels like it's made of red splinters with sharp edges, and they're slicing me up from inside"), Gwen is still trying to unravel her grandfather's riddle and figure out what it was he hid before he died. No, I'm not going to mention what it is, but it's a game-changer that only makes her job more perilous. 
 She also finds that the price for closing the Circle may be more than it's actually worth -- but the Guardians are okay with that price, even if it means someone's death. And the sinister Count Saint-Germain is still plotting something with a secret accomplice, which Gwen must uncover before she runs out of time. 
 "Emerald Green" is not one of those really devastating finales to a trilogy/series -- it's more the kind that wraps things up nicely, and gives you a satisfied glow afterwards. The beginning of the book is a bit rough, since it's mostly either Gwen moping or bouncing around through time, but it picks up as her time-hopping quest finds a focus. 
 And Kristen Gier's writing is strong and breezy, with bursts of beautiful description ("shimmering birds of paradise, leaves, and flowers in shades of blue and silver twined their way over the brocade bodice") and a pleasant undercurrent of gentle humor (Xemerius is hilarious, as always"). She answers some fairly important questions about time travel, and manages to answer some important questions about Gwen as well. 
 The biggest problem is the romance -- while it's nice to see a teen girl's heartbreak NOT being depicted as the end of the world (Gwen fantasizes about dying picturesquely of a broken heart... then amends, "But first I had to go to the toilet, urgently"), Gideon's arrogance and Gwen's jealousy taint the romance. That said, the book has a LOT going on besides the romance, so you can sort of overlook it. 
 When she isn't around Gideon, Gwen is a pretty entertaining heroine -- snarky, enthusiastic and trying to juggle an overcomplicated life. When she isn't time-traveling, she has to deal with mean-spirited relatives and getting stabbed during a duel. Gideon is a less developed character, with a few too many face heel turns, but the other characters tend to be more entertaining and fleshed-out... especially the gargoyle. 
 There are some flaws in this jewel, but "Emerald Green" is still a sprightly, fast-moving fantasy story, with some clever twists and magnificent writing. It certainly leaves me wondering what Gier will bring us next.