Melissa Scott and Lisa Barnes have written some great magical books together (Point of Dreams and Point of Hopes). This book precedes those two. I preferred those stories to this one which is set in 1593 in Engand when Elizabeth was Queen and James VI was King of Scotland. Add witches and Satan to the plot and, personally, I just don't care for that.
The heavy summer air of 1593 is full of portents for Elizabeth, England's Queen, and James VI, King of Scotland. A coven of witches secretly controlled by the Wizard Earl of Bothwell has summoned a storm to sink the ship that bears James bride to Scotland. Though the ship made port, the success of their summoning has emboldened them; the coven is now launching wizardly attacks on the King himself. The King has his protectors - not least the Queen of England herself - but not even Elizabeth's secret service and her champion, the redoutable Sir Philip Sidney, can be on watch every instant. Eventually a trap is sprung, and King James is at the mercy of the satanic Bothwell's deadly spells.