Children of the Serpent Gate: Book 3 of The Tears of Artamon

At the start of the rousing conclusion to Ash's fantasy trilogy (after 2004's Prisoner of the Iron Tower), King Enguerrand of Francia has the five Tears of Artamon, the magical jewels that give their possessor claim to Novaya Rossiya. This means a crisis for Novaya Rossiya's Emperor Eugene, particularly since the Francians have kidnapped his chief magus, Kaspar Linnaius, and are going to burn him at the stake.