On a moonlit road in Hampstead, Walter Hartwright meets a young woman - beautiful, terrified and dressed entirely white - alone on the street. Compelled to help this woman, he finds himself caught up in a world of secrets, murder and madness, with an impossible mystery to solve. The odds seem stacked against him, but a sleuthing partnership with the brilliantly clever Marian Halcombe may be just enough to outwit their formidable nemesis - the menacing Count Fosco.