Prince Caspian is the second published (fourth chronologically) book in C.S. Lewis's The Chronicles of Narnia. The four Pevensie siblings—Peter, Susan, Edmund, and Lucy—are mysteriously recalled to Narnia 1,300 years after their first reign. They join forces with the rightful heir, Prince Caspian, against his tyrannical uncle, King Miraz. They must restore the old Narnia, with the help of the noble lion, Aslan. The "rack" likely refers to a specific, inexpensive bookstore edition.
