Thus reads Wikipedia:
In Historic Doubts on the Life and Reign of King Richard III (1768), Walpole defended Richard III against the common belief that he murdered the Princes in the Tower. In this he has been followed by other writers, such as Josephine Tey and Valerie Anand. This work, according to Emile Legouis, shows that Walpole was "capable of critical initiative".
A while ago, I actually read the book in question and it seemed like an impressive piece of research. However, I haven't been able to find serious scholarly engagement with Walpole's work. Could it be that no professional historians noticed his well-known book for ~250 years? Or am I not looking at the right place? (I tried Google Scholar.)
UPDT: The bounty is expiring soon... hurry up... :)