Josephine Tey's Novel "The Daughter of Time" addresses which historical mystery?

Josephine Tey was the pen name of Elizabeth MacKintosh (1896-1952) a Scottish detective writer and dramatist. Before turning to full-time writing she worked as a teacher and a nurse.

"The Daughter of Time" was her last novel, and one of her most famous. It includes her serial character, Detective Alan Grant. In this work he is confined to bed with a broken leg, and also suffering from chronic boredom. A friend proposes he amuses himself by investigating an historical mystery, and he chooses Richard III, then, not least as a result of Shakespeare's presentation of him, seen as a murderous villain who was to blame for the deaths of the Little Princes in the Tower to ensure he acceded the throne.

Grant prides himself on reading faces, and decides that Richard's is not the one of a villain. He carries out further research, enlisting the help of an American researcher, and comes to the conclusion that the Tudors (Shakespeare's patrons!) covered up the fact that it was far more likely to have been Henry VII, founder of the Tudor Dynasty after Richard's death on Bosworth Field, who was to blame for the infanticide, and that Richard was a good king.

She was not the first to suggest this, but was certainly out of step with mainstream thinking.

Ironically, things have now done a complete volte face, and Richard (whose remains have been discovered in a Leicester car park and genetically verified) has undergone an historical rehabilitation.