The Wishsong of Shannara by Terry Brooks is the third novel in The Original Shannara Trilogy. The story features Jair and Brin Ohmsford, the children of Wil Ohmsford and Eretria from The Elfstones of Shannara. The siblings, each possessing an inherited magic, must save the Four Lands from the evil magic within a tome called the Ildatch.