Archibald Lox and the Pick of Loxes: Archibald Lox series, book 8

When Archie finds himself trapped in a claustrophobic zone from which there seems to be no escape, he's thrown a lifeline by the most unlikely of allies. A showdown with a troubled royal ends in chaos and betrayal, and Archie is abducted and imprisoned in a cold, forgotten area of the Merge. With a collection of fellow locksmiths, Archie is set to work on an apparently unpickable lock, but if he manages to do what no other Lox has achieved, he might also seal his doom... Book eight of the Archibald Lox series by Darren Shan, the New York Times bestselling author of Cirque Du Freak and Lord Loss.