When builders renovating a café in King's Lynn unearth a human skeleton, they call for DCI Harry Nelson and Dr Ruth Galloway, Head of Archaeology at the University of North Norfolk. Ruth is preoccupied with the threatened closure of her department and by her ever-complicated relationship with Nelson.
The bones are identified as those of Emily Pickering, an archaeology student who went missing in the 1990s. Emily attended a course run by her Cambridge tutor. Suspicion falls on him and on another course member - Ruth's friend Cathbad, who is still frail following his near death from Covid. As they investigate, Nelson and his team uncover a tangled web of relationships within the student group and the adults leading them. Then, just when the team seem to be making progress, Cathbad disappears.
The trail leads Ruth and Nelson to the Neolithic flint mines in Grime's Graves. The race is on, first to find Cathbad and then to exonerate him, but will Ruth and Nelson uncover the truth in time to save their friend?