Shortly after learning his brother-in-law, Will Clark, was murdered, Simon Maldon is called into Queen Elizabeth's presence. Trusting her old friend's judgment, the queen wants Simon to go with her delegation to Scotland and make an objective assessment of the character of Mary, Queen of Scots. Despite his pleas of family concerns, Elizabeth insists he must go. Reluctantly, Simon obeys his monarch's command. After Simon sails for Scotland, his son Henry, wife Hannah, and old friend Calkin delve into the mystery of Will Clark's murder. They soon face a killer determined to hide his crimes and willing—even eager—to murder again to do so. In Scotland, Simon faces his own trials. An outlaw captures the Englishmen and threatens to kill them if they don't abandon their mission. In order to thwart the outlaw's grandiose scheme, Simon must escape a dungeon tower, rescue his companions, and lead them to Edinburgh with all possible speed. For a London apothecary with no knowledge of the wild countryside, Scotland itself is part of the problem. Will the rough folk of the Marches help, or will they turn their backs and let the Englishman make his way as best he can?