Gerda malaperis!

 () is a novel by Claude Piron, one of the most famous novels in Esperanto literature.
In the novel, dialogue begins simply and progresses in difficulty using everyday vocabulary (with word-lists available in various languages). It is suitable for beginners trying to improve their grasp of the Esperanto language, and includes rehearsal of basic grammar and an entertaining story.
The mystery begins when three college students witness the strange disappearance of Gerda, a woman who is an expert in 'cryptic languages'.
Published as a book, "Gerda malaperis!" has since been incorporated into electronic courseware. A movie is available on DVD.