The headmistress of Cresacre Abbey School has asked Phineas Fox to establish whether an opera, to be performed as part of the school's bicentenary celebrations, plagiarises an earlier work. During the course of his investigations, Phin discovers that curious legends about the school's past still linger, including the fate of a group of nuns who disappeared without trace more than 200 years before. What exactly happened to them? And who is the mysterious...

"When music researcher Phineas Fox is asked to verify the contents of an old scrapbook, rescued from the site of the historic Chopin Library in Warsaw, he is initially sceptical. But he soon discovers an intriguing link between the Library and an infamous piece of music known as the Dark Cadence. Legend has it that the Dark Cadence was only performed at a traitor's execution - and it has never been written down. It is believed to have last been played...