This Audio App has been the object of a hunt which has extended from Manila to Berlin, and from Italy to Chile, for four hundred and fifty years. The patient research of scholars, the scraps of evidence found in books and archives, the amazingly accurate hypotheses of bibliographers who have sifted the material so painstakingly gathered together, combine to make its history a bookish detective story par excellence. It is easy when a prisoner has been arrested and brought to the dock to give details of his complexion, height, characteristics and identifying marks, to fingerprint him and to photograph him, but how inadequate was the description before his capture, how frequently did false scents draw the pursuer off the right track! It is with this in mind that we examine the subject of this investigation, remembering that it has not been done before in detail.