Fosse House, home of the reclusive Luisa Gilmore, harbours curious secrets - secrets that stretch back almost a century, to the ill-fated Palestrina Choir in its remote Belgian convent.

When Oxford don Michael Flint travels to the house to trace the origins of the long-dead Choir, he is at once aware of the house's eerie menace. Who is the shadowy young man who lurks in the grounds, and why does his exact likeness appear in a sketch from 1917? What is the strange whispering that echoes through the corridors? And why is Luisa so afraid when a storm makes it necessary for Michael to spend the night inside the house?

Back in Oxford, when Nell West uncovers the story of the infamous 1917 'Holzminden sketch' - the lost, legendary drawing from World War I - a dark fragment of the past begins to stir. A fragment that Michael, in the lonely old house, may not be able to resist.