Marian and her sister Laura live a quiet life under their uncle's guardianship until Laura's marriage to Sir Percival Glyde.

Sir Percival is a man of many secrets - is one of them connected to the strange appearances of a young woman dressed all in white? And what does his charismatic friend, Count Fosco, with his pet white mice running in and out of his brightly coloured waistcoat, have to do with it all?

Marian and the girls' drawing master, Walter, have to turn detective in order to work out what is going on, and to protect Laura from a fatal plot...