Or eighth, if you count "Out of the House of Life", which is primarily a book about Madeline de Montalia, but includes some of Saint-Germain's history. Or eleventh, if you also include "A Flame In Byzantium", "Crusader's Torch", and "A Candle For d'Artagnan", which are almost entirely about Olivia Atta Clemens, and therefore properly a spinoff series of their own.
The series to date (the date of the writing of this book, not the writing of this review) is: "Hotel Transylvania", set in the mid seventeen hundreds in France; "The Palace", set in Florentine Italy in the time of Botticelli; "Blood Games", set in the imperial Rome of Nero (and slightly beyond); "Path of the Eclipse", set around 1200, in China, India, and the middle east; "Tempting Fate", set in Germany between the twentieth century's world wars; "The Saint-Germain Chronicles", a collection of short stories set from 1880-1981; the aforementioned "Olivia" trilogy (Olivia was Saint-Germain's love interest in the book "Blood Games") set respectively in 6th century Byzantium, late 12th century Europe, and 17th century France; the aforementioned "Out of the House of Life", which features Madeline (the love-interest from "Hotel Transylvania") in early 19th century Egypt, with occasional flashbacks to Saint-Germain's days in ancient Egypt, circa 1000 B.C.E.; and this book, in many ways the best of the lot.
This book is set in late 16th century Russia, during the reign of Ivan IV (The Terrible) and that of his son, Feodor. As usual, Yarbro's historical research is impressive; I'm not sufficiently educated on the subject to vouch for any of her books' history, but it certainly feels right, and meshes with what little I DO know from other sources. Also as usual, her plot is excellent and her main characters are a delight. What sets this book apart from most of her previous entries in this series is that her villains are much less cardboard; usually, her villains have been simply blatantly evil, from diabolists in Paris to insane worshippers of Kali the death-goddess in Persia to Nazis in Germany. Now granted, all of these sorts of people existed, but their motives generally weren't as one-dimensional as these stories have generally made them. They were generally more like the villains in this book: a hypocritical Jesuit who resents Saint-Germain for his successes and talents, and for being independant of his authority, and various ambitious nobles looking to improve their own situation at anyone and everyone else's expense.
For those new to the series, Saint-Germain is a vampire who has lived for something on the order of 3500-4000 years, and so each book gives us a look into another period in the life of an immortal. The series is probably more interesting to fans of historical fiction that traditional vampire fans, as the vampiric aspects are much reduced from what one usually sees. The writing is very good, and the main character is a delight.