Hetty and Robert arrive home after a long break with their son Derek and his family in Australia. Geoff and Janet have been minding the agency and Hetty has scarcely unpacked before she gets embroiled in a new case about hidden treasure. She and Geoff have been asked by Moira Pridwell to find a book written by her husband, who died in a recent explosion at the iron ore mine where he worked in Cumbria.