I have many unusual and relatively unknown books in my library that are extremely valuable. Two examples are: Discovering the End of Time: Irish Evangelicals in the Age of Daniel O’Connell (McGill-Queen’s University Press, 2016), and Exporting the Rapture: John Nelson Darby and the Victorian Conquest of North-American Evangelicalism (Oxford, 2018), both by Donald Harman Akenson. We all know, or we should know, about John Nelson Darby (1800-1882), and how he popularized dispensationalism 
years before the Scofield Reference Bible (not invented it as many of the Reformed falsely assert). Although there is much in these books about Darby and his teachings and writings, they primarily explore the religious and cultural environment in which Darby lived in Ireland. These books are absolutely essential for understanding the life and times of John Nelson Darby.