One of the most striking parts of Robert Penn Warren’s novel All the King’s Men is Chapter 4, in which narrator Jack Burden tells the story of his distant relative Cass Mastern. A Confederate soldier, Mastern betrays his best friend by falling in love with the man’s wife and then out of guilt tries repeatedly to get killed in battle but ironically becomes a hero for his daring, before finally attaining a mortal wound. In The Cass Mastern Material, James A. Perkins fully explores how this episode supplies the crucial piece to a puzzle surrounding Warren’s novel, tracing the story’s evolution through several versions and genres over almost twenty years. Found here are both the earliest, short-story rendition of the Cass Mastern episode, originally published in 1944, and Warren’s final dramatic version, completed in 1961 and now made available in print for the first time. The play was finally staged in 1999, and Perkins appends related letters, production notes, and an interview that provide a context for understanding the work’s importance in Warren’s career. I have always felt that the section is central to [All the King’s Men], Warren wrote, concerning the Cass Mastern material. This unique volume affords a view of Warren’s restless creative process and throws new light on the story that formed the core of his masterly novel.