For some fun starting points on the history of both the Princes in the Tower and their pretenders, Lambert Simnel and Perkin Warbeck, check out the following:
Audrey Williamson, The Mystery of the Princes: an Investigation into a Supposed Murder (Sutton Pub Limited, 2002).
Francis Bacon, History of the Reign of King Henry VIII (University Press, 1885). Full Text.
James Gairdner, History of the Life and Reign of Richard III, (including) The Story of Perkin Warbeck (Longman, Greens, & Co., 1879). Full Text.