Stolen Knight - Knights of Kilbourne, #4

Purloined magic. A mysterious jewel. A demonic menace. The world in the balance. Not exactly the way Morgan and Marissa intended to spend their honeymoon. Married at last. And shipwrecked. A storm on the Thundermist Sea has cast newlyweds Morgan and Marissa onto the shores of Parthane. This exotic land boasts ancient temples, sumptuous feasts, court intrigue.and deadly danger. But it's all part of a plan.
The dauntless pair has been dispatched to recover a priceless jewel stolen from the wizards of Caerfaen by Prince Azim of Parthane. The ruby, known as the Demon's Fire, is not merely beautiful and valuable, but is also a magical artifact which gives whoever wields it access to unimaginable power. Power which, in the wrong hands, could lead to a catastrophe of demonic proportions. As Royal Enchantress (and possessor of an ancient grimoire), Marissa is the only hope to retrieve the jewel.
There's no way Morgan will allow Chief Wizard Foxwent to send his new bride off to Parthane alone and unprotected, but he'll need to call on all his skills and instincts to keep them safe in this new world of decadent temptations and lethal double-crosses. The book and the jewel are somehow bound together, and their confluence might turn both Parthane and Kilbourne into magical wastelands. Morgan and Marissa must outwit ghostly guards, malevolent magicians, and an impregnable palace to steal back the jewel and return it to Kilbourne.
They'll only have one chance to complete their mission, and failure might just mean the end of the world.