Walking in Darkness is a memoir written by the Auror Alastair Van Harkwood. The book includes a description of the Patronus Charm: The wizard must bring vividly to mind his most cherished, happiest memory. It is extraordinarily difficult for those less talented than myself, and I have never known another man who did not require a mentor before the first silver tracery of his Patronus could be seen. A copy of the book was given to Alexandra Quick as a birthday gift in March of 2011.