Gregor and the Code of Claw is the fifth and final book in the Underland Chronicles series. It was published in the U.S. in 2007 by Scholastic Press.

Soon after the events of Marks of Secret, Gregor returns to Regalia, faced with a new prophecy and a deadly role to fulfill as the Warrior.

As he fights to help his friends, Gregor faces many challenges regarding Solovet. His actions are closely watched by her and her spies, making it difficult to fight when he wishes, although his recklessness may lead to complications and difficulties.

While the war rages on, the Code of Claw has yet to be cracked, leaving the Underlanders at a disadvantage.

With Gregor's fate set in stone, the Underland is left at the mercy of Sandwich's vision, a team of Code Breakers, and a young boy destined to fight at the cost of his own life.