Die drei Fragezeichen (Hörspiele) is a 138-book series with 138 released primary works first released in 1964 with contributions by Robert Arthur, Alfred Hitchcock, Jens Wawrczeck, William Arden, M.V. Carey, Nick West, Marc Brandel, Megan Stine, Henry William Stine, G.H. Stone and 11 others.