In 1939 the Vicar, the Rev. Harold S. Goodrich, decided to have the interior of the church cleaned and redecorated. Before all this work was done, the architect in charge of the work … wisely decided to have the walls inspected in case the plaster was medieval and retained any traces of painting. I [Clive Rouse] was called in to undertake this, and on making tests evidence of very extensive mural decoration immediately came to light. 

In The Church of St John the Evangelist, Corby, Lincolnshire, and its mural paintings (1941; printed for private circulation by Strangeways Press Limited), a book ‘written as a gift to the Church’, E. Clive Rouse describes the process of uncovering and preserving the paintings, and includes full colour plates of detailed watercolours to help interpret them. 

From this page you can download a pdf transcription of the text of that book, with embedded photos of the prints.