The Hitchhiker's Guide to the Galaxy Radio Scripts: Tertiary, Quandary and Quintessential Phases is a book containing the fourteen scripts from the Tertiary, Quandary and Quintessential phases for The Hitchhiker's Guide to the Galaxy radio series. This collection of scripts was first published in 2005 by Pan Books, who published other books from the Hitchhiker's series.
The scripts for these phases of the radio series were adapted from the third, fourth, and fifth books in the Hitchhiker's book series: Life, the Universe and Everything, So Long, and Thanks for All the Fish, and Mostly Harmless. However, they also included new material written especially for the radio sequels, and a Complete Cast and Production List section at the end of the book.