The Sword Thief is the third book in The 39 Clues series. It was written by Peter Lerangis and was published by Scholastic on March 3, 2009. The Sword Thief follows the first two books in the series, The Maze of Bones by Rick Riordan and One False Note by Gordon Korman.
The book starts with Dan and Amy in a Venice airport. There, Ian and Natalie Kabra steal their plane tickets and board a plane where their au pair, Nellie who is already on the plane. Then, Amy and Dan are then forced to team up with Alistair Oh and fly with him on his private plane to Japan. Together they learn about Toyotomi Hideyoshi, the greatest warrior in the history of Japan, and the son of the first Tomas. The Holts kidnapped Amy, Dan, and Alistair and threatened them into helping them find the next clue.
In every book in the series, there is a code written in the page numbers. The one for this book is written in symbols, which reads "The competition is about Hope". Hope is also the name of Dan and Amy's mother, Hope Cahill.