The Echidna's Scale — Jeffrey Quyle

Book Two in the Alchemy's Apprentice Series. Marco is about to enter the stage of great happiness in life, he thinks. He has been given a castle and a noble title by the Duke of Barcelon, and he has the most beautiful woman in the world as his beloved fiancee. They have a wedding planned for the upcoming spring, and they are happy together. He has his alchemy to dabble in and work on. Life could not be better.
But a pair of serious accidents forces him and Mirra's brother Glaze to travel to the Isle of Ophiuchus. And even though he is miraculously healed at the temple atop the island, he is given a commandment by the spirit of the island - he is sent on a deadly and arduous quest to recover a scale from the mythical monster, the Echidna, though he doesn't even know where the monster is, or even what it is.
He and Glaze and their unwilling new companion, Porenn, the acolyte of the island who Marco has met before, begin on their way to find out how to proceed with his quest. But before they even finish the first stage of the journey, they find complications and difficulties that will thwart Marco's plans for a straightforward journey.
A long dangerous trip, through the wintertime mountains, will test Marco and his companions. And he'll be forced to travel with watchdogs who keep an eye on him, and tempt him to stray at the same time. Even finding success brings surprising twists in Marco's plans, and by the end of the his story, Marco won't know what his future holds, except another journey.