Sophie Scholl – Die letzten Tage (The Last Days) by Fred Breinersdorfer, published by Fischer in 2006 (in German); the book that provided the motivation for writing The Signs of a Mystery (TSOAM).
"Es lebe die Freiheit!" ("Long Live Freedom!") by Ulrich Chaussy and Gerd. R. Ueberschär, published by Fischer in 2013 (in German). This book contains a detailed discussion of each leaflet campaign by the White Rose resistance group, together with the complete transcript of each interrogation by the Gestapo.
Joan of Arc – In Her Own Words compiled and translated by Willard Trask, published by Books & Co in 1996. Thematically related to the previous book; contains the complete transcript of Joan's interrogation at her trial.
Sophie Scholl and the White Rose by Annette Dumbach and Jud Newborn, published by Oneworld in 2006.
Living Through the Blitz by Tom Harrison, published by Penguin in 1978. This compilation of contemporary diaries and interviews bypasses both the wartime propaganda as well as the post-war clichés and lets those who lived through these terrible years speak for themselves.
The Blitz by Juliet Gardiner, published by Harper in 2011. Historical account of the Battle of Britain.
Below Freezing – The Antarctic Dive Guide by Lisa Eareckson Trotter, published by Wildguides in 2008.
The Effects of Low Temperature on Biological Systems by B. W. W. Grout and G. J. Morris (Eds.), published by Edward Arnold in 1987. Provides an introduction to cryobiology such as it was at the time of Siobhán's visit to Antarctica.
Animal Life at Low Temperature by John Davenport, published by Chapman & Hall in 1992. Another university-level text on cryobiology that is contemporary to the novel.
Animal Communication Theory by Ulrich E. Stegmann (Ed.), published by Cambridge University Press in 2013.
Echolocation in Bats and Dolphins by Jeanette A. Thomas, Cynthia F. Moss, and Marianne Vater (Eds.), published by University of Chicago Press in 2004.
Moray Firth Dolphins by Tim Stenton, published by Bassman Books in 2013.
Witchcraft and Magic in Europe – The Twentieth Century by Willem de Blécourt, Ronald Hutton, and Jean La Fontaine, published by Athlone Press in 1999. Covers different aspects of Paganism, Witchcraft, and Satanism, including a detailed account of the Satanic ritual abuse scare of the 1980's.
The Oxford Handbook of New Religious Movements by James R. Lewis (Ed.), published by Oxford University Press in 2008. Addresses a wide range of subjects, including the subversive techniques employed by different cults.
Grimoires – A History of Magic Books by Owen Davies, published by Oxford University Press in 2010. A comprehensive academic account of all types of books of magic spells.
The Book of Grimoires – The Secret Grammar of Magic by Claude Lecouteux, published by Inner Traditions in 2013. More hands-on than the previous book, with many practical instructions on how to cast different spells.
A Brief History of Time by Stephen Hawking, published by Bantam in 1996. This is an illustrated and expanded edition of the classic from 1988.
On Signs (Part 3, Chapter 2 of Opus maius) by Roger Bacon, published by Pontifical Institute of Medieval Studies in 2013. One of the earliest discussions of semiotics, originally submitted to Pope Clement IV in 1267.
A Theory of Semiotics by Umberto Eco, published by Indiana University Press in 1979.
Readings in Zoosemiotics by Timo Maran, Dario Martinelli, and Aleksei Turovski (Eds.), published by De Gruyter Mouton in 2011. A collection of university-level essays that extend the subject of semiotics from humans to other animals, including marine mammals.
The Masks of God – Primitive Mythology by Joseph Campbell, published by Souvenir Press in 2011. Originally published in 1959, this is still the definitive work on the underlying similarities between different religious belief systems.
Pagan Britain by Ronald Hutton, published by Yale University Press in 2014. Covers the palaeolithic period up to the conversion to Christianity.
The Occult Roots of Nazism by Nicholas Goodrick-Clarke, published by Tauris Parke in 2009, first edition in 1985.
Black Sun by Nicholas Goodrick-Clarke, published by New York University Press in 2003. The sequel to The Occult Roots of Nazism, discussing the evolution of Nazi ideology in the post-war period, ranging from New Atlantis to Nazi UFO's on Antarctica.
The Ice Museum – In Search of the Lost Land of Thule by Joanna Kavenna, published by Penguin in 2005.
Wagner's Ring of the Nibelung by Stewart Spencer and Barry Millington, published by Thames & Hudson in 2013. Provides an introduction to the background and thematic content of the four operas, together with a complete English translation of the libretto.
Color Illustrations for Wagner's "Ring" by Arthur Rackham, published by Dover in 1979.
Towers in the North – The Brochs of Scotland by Ian Armit, published by the History Press in 2011.
Geheimprojekt Atombunker – Die Troposphären-Funkstation Eichenthal by Götz Thomas Wenzel, published by Ch. Links in 2006 (in German). A description of the East German military tropospheric radio stations and their history.
Hitler's Pre-Emptive War – The Battle for Norway by Henrik O. Lunde, published by Casemate in 2009.
U48 - Das erfolgreichste U-Boot des 2. Weltkrieges by Franz Kurowski, published by Flechsig in 2013 (in German). A detailed description of the Type VIIB German submarines of the Second World War.
Island of Barbed Wire by Connery Chappell, published by Hale in 2005. A description of life in the women's internment camp on the Isle of Man during the Second World War.
Other Media
Sophie Scholl – Die letzten Tage (The Last Days) by Marc Rothemund, released in 2005, 115 min, German with English subtitles; based on the biography of the same name by Fred Breinersdorfer (see above).
The Nazis – A Warning from History by the BBC, first broadcast in 1997, 289 min; documents the rise of the National Socialist party after the First World War.
A Year to Remember – The 1930s to 1980s by Pathé, released in 2011, 10 hrs for each decade; documents the period covered by TSOAM through a compilation of daily news reports; history as it was experienced at the time.
Wagner and Me by Stephen Fry for the BBC, first broadcast in 2010, 89 min; an introduction to Richard Wagner, with a special emphasis on the role his music played during the Nazi era.
The Ring Without Words – Orchestral Highlights from the Ring Cycle, recorded by Lorin Maazel with the Berlin Philharmonic Orchestra for Telarc in 1988, 70 min (the complete Cycle takes about 14 hrs to perform on stage).
Ocean Giants by the BBC, first broadcast in 2011, 3 episodes of 60 min each; documents the role sound plays in the lives of whales and dolphins.