Doctor Who Discovers Historical Mysteries

Doctor Who Discovers Historical Mysteries was the sixth in Target Books' Doctor Who Discovers series of books commissioned to be written by the Fourth Doctor during his time working with UNIT.

The Doctor had begun work on this book, but left it unfinished until a robot sent by the publishers from the 64th century invaded the TARDIS to forcefully remind the Fifth Doctor of his contractual obligation; the Doctor therefore resumed investigating the mystery of who killed the Princes in the Tower during the reign of King Richard III of England. In the course of the adventure William Shakespeare died in the century before his birth, which cause the robot's deadline circuit to malfunction; the robot then exploded. Unable to write about the truth of what happened to Richard and the princes in order to preserve the course of history, the Doctor suggested the possibility of investigating the historical mystery of Jack the Ripper instead. (AUDIO: The Kingmaker)

Behind the scenes
In the real world, only five books were published in the Doctor Who Discovers. A sixth, Doctor Who Discovers Pirates, was written but shelved as part of the cancellation of the series due to poor sales.