The Knave of Diamonds — Roberta Olsen Major

Twins Jillian and Julian have been Prince Jacot's best friends all their lives. They have laughed at his antics, helped him out of scrapes, and wondered if he would ever really grow up. When the Queen of Coalveign becomes deathly ill, Jacot must look to his strengths, and rely on his friends, as he embarks on a dangerous journey to save his mother's life.