In 1846 Darwin had a secret: an essay sealed in an envelope and locked in his study drawer which would overturn human understanding of time and nature forever. Before he published, he had just one more riddle to solve, that of the strange anatomy of a barnacle, nick-named Mr Arthrobalanus, found in South America during the voyage of the Beagle. Abberant creatures like these are the key to the processes of natural selection, but eight years later, with a study filled with hundreds of barnacle specimens, the case is still unclosed. Was Darwin hesitating? Or was he testing his "dangerous idea" to destruction? "Darwin and the Barnacle" is the story of how genius sometimes proceeds through indirection - and how one small creature contributed to history's most spectacular scientific breakthrough.