When a ghostly figure is sighted in the murky tunnels beneath Edinburgh, Zinnie and her sisters suddenly find their underground home filled with curious visitors. Among them is the owner of a new museum – The House of Hidden Wonders – who seems to know more about the 'ghost' than he should. As Zinnie discovers dark secrets concealed within the so-called House of Wonders, she throws herself into a world of intrigue, determined to uncover the real story behind the ghost. Can she shine a light on the truth or will the sinister forces against her prove too strong?