Dunkelgraf mystery
By: by O.V. Maeckel with the collaboration of Mrs. Aubrey Le Blond.
Contributors: Le Blond, Elizabeth Alice Frances.
Publisher: Hutchinson & Co.
Published: 1929
Place of publication: London
Language: eng
Subjects: Valck, Leonardus Cornelius van der.; Angoule me, Marie The re  se Charlotte, -- duchesse d'.
Notes: Limited ed. of 500 numbered and signed copies.

The author identifies the "Dunkelgraf" as Leonardus Cornelius van der Valck and the "Dunkelgra fin" as Marie The re  se Charlotte, daughter of Louis XVI.