on one story in the Doctor Who collection The Shakespeare Notebooks, an academic researching Julius Caesar is stalked by a menacing figure the writer calls Mr. Silhouette- who is this character? What are his (its) goals?
In footnote28, the annotator is advised to look up Appendix 4 to Smith's Syllables and Sonnets 3rd edition.
Appendix 4, explains that the book is a psychic trap, the imprinted form of an evil mind: footnote29 suggests by juxtaposition with the text on which it comments Mr Silhouette is a form of ghost.
The ending indicates that he's the ghost of Duluth, the author of the Duluth Quarto. "His face looks familiar I open the Duluth Quarto. Just to go to the frontispiece, the engraving of Duluth himself. It's that same face."
Reading the text of Julius Caesar 'within the Quarto' gives an account not of the fall of Rome, but of the fall of the Capitol of the Time Lords during the Time War, during which ghosts shriek in the streets.
"Duluth" is not a reference to something else within Doctor Who, but may be a name of one of the defenders of Gallifrey in the time war. As seen in 'The End of Time' etc those under Rassilon at the end were not benevolent. [In the Doctor Who tie-in material the Master is recalled to Gallifrey during the 'War in Heaven' the future time war in the EDAs that prefigures the Time War in the 21st century TV series, as were other renegade Time Lords.]
As a ghost [implicitly] Mr Silhouette may have no goals as such, only a hunger for the living. But reading the book will let "his black soul...out into the world".