Thruppence and Tim don't know what they're getting themselves into when they ring the bell at the house with dusty windows and a tarnished name plate to enquire about the advertised 'Saturday Person'. What could be so difficult about an unspecified Saturday job? Well, had that name plate been properly cleaned, Thruppence and Tim might not have been so keen to enter...Pressured by the stern Minister Beeston from the Department of Economies, the Ministry of Ghosts has been given three months to prove the existence or non-existence of ghosts or else it will be shut down! As it seems that children are particularly magnetic to ghosts and supernatural beings, Thruppence and Tim are added to their ghost-catching team. And although neither of them are scared by talk of ghosts or monsters, they couldn't have imagined the truth behind what they will find...