This discussion of the religious and other teaching in the 'N-Town' plays is supported by close examination of the complex manuscript. I show that the scribe who wrote most of the plays worked in three stages:- first the text from the start of the Passion to the Last Words, then the rest of the plays, and finally substantial revision of this initial recension; some decades later a reviser amended sections of text, apparently for performance. Catechetical teaching and exceptional Marian devotion feature in all stages of compilation and recension. After considering the state of the codex before the present binding, I argue that it comprised several subsidiary booklets until the later 17th century. The writers of individual plays are shown to have used a number of orthodox sources, two of which have not been identified before. The Ten Commandments follow a late 14th. century summa called Cibus Anime and the Passion uses an extended (rather than the original) version of the Northern Passion. The importance of Peter Comestor's Historia Scholastica is greater than previously noted, and anti-heretical features of Nicholas Love's Mirror of the Blessed Life of Christ may be specially significant. All the identified sources are discussed in general terms (including their respective availability), and I examine how in adapting them the compilers avoided material with no scriptural provenance. Considered as a whole the sources imply that those who worked on the plays were regular clerics. Features of the catechetical and other teaching are considered separately, i.e. the Trinity, the Seven Deadly Sins, the Decalogue, the Seven Sacraments (both as a theological concept, and individually in the case of Baptism, Confession, Matrimony, and Eucharist), Mercy, and lay obligations. The teaching is reinforced by the treatment of obedience which, although present in all but two of the plays, is treated differently in the Passion episodes which take a theological view of the authority to which obedience is due. In order to contextualise the findings evidence for location is reviewed. Whilst the results of dialect analysis are broadly consistent with the generally acknowledged scribal origins in southern Norfolk, previously unnoticed textual evidence links two sections of interpolated material with Norwich, where I suggest the Carmelite priory as a possible place of origin. After reviewing Lollardy in the region I conclude that the plays respond to known heretic positions only as part of a wider address to the lay community as a whole.