The Last Remains (Dr. Ruth Galloway 15) by Griffiths Elly

When builders renovating a café in King's Lynn find a human skeleton behind a wall, they call for DCI Harry Nelson and Dr Ruth Galloway, Head of Archaeology at the nearby University of North Norfolk. Ruth is preoccupied with the threatened closure of her department and by her ever-complicated relationship with Nelson. However, she agrees to look at the case.
Ruth sees at once that the bones are modern. They are identified as the remains of Emily Pickering, a young archaeology student who went missing in the 1990s. Emily attended a course run by her Cambridge tutor. Suspicion falls on him and also 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. What was the link between the group and the King's Lynn café where Emily's bones were found?
Then, just when the team seem to be making progress, Cathbad disappears. Was it guilt that led him to flee?
The trail leads Ruth and Nelson to the Neolithic flint mines in Grimes Graves which are as spooky as their name. 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?