A Dark so Deadly is a novel by Stuart MacBride which is set in the fictional town of Oldcastle. Whilst this is a stand alone novel, its setting of Oldcastle and the use of one of its characters, Dr Alice MacDonald, provide a link to the two Ash Henderson novels (Birthdays for the Dead and A Song for the Dying). A Dark so Deadly was the first novel in a run of seven books for Stuart MacBride not to have debuted at number one in the book charts.