Will has always dreamed about becoming a knight like his father who he never knew, but, when he is rejected by the Castle Redmont's Battle School, he becomes an apprentice to Halt, the mysterious Ranger instead. Will reluctantly becomes adept at using the Ranger's secret weapons and later discovers their usefulness during a mission to prevent the king's assassination.

In this prequel to the Ranger's Apprentice series, Halt and Crowley travel north seeking Prince Duncan's royal warrant to stop Morgrath from corrupting the Corps, but if they are to prevent a coup that is nearing success, the young Rangers will have to tread a dangerous path toward the annual tournament at Gorlan.