Who Murdered Chaucer?: A Medieval Mystery, Terry Jones, Robert Yeager, Terry Dolan, Alan Fletcher, and Juliette Dor (Thomas Dunne Books, 2003)
Richard II and the Revolution of 1399, Michael Bennett (Sutton, 1999)
A History of the County of Gloucester, vol. 2, (originally published by Boydell & Brewer Ltd., 1907):
http://www.british-history.ac.uk/vch/glos/vol2/pp. 79–84