The Daughter of Time
(Penguin, 1981 edition of 1951 story)
I had, as I suspected, read this before. Tey specialises in historical crime novels in which the past is uncovered layer by layer (there was a lovely one she did about son coming back from the dead - Brat Farrar - which is allegedly being filmed with Brad Pitt in the lead). In The Daughter of Time, a police detective laid up in hospital sets out to find out whether Richard III did kill the Princes in the Tower. This is historical research, the process of it, laid out in the forensic police procedural style and a light easy read. There is even a nod to the parallel between criminology and writing, in that a character within the novel plans to write a book about the process of the policeman discovering the past from his hospital bed.