The discovery of a missing woman's bones forces Ruth and Nelson to finally confront their feelings for each other as they desperately work to exonerate one of their own. When builders discover a human skeleton while renovating a café, they call in archaeologist Dr. Ruth Galloway, who is preoccupied with the threatened closure of her department and by her ever-complicated relationship with DCI Nelson. The bones turn out to be modern—the remains of Emily Pickering, a young archaeology student who went missing in 2002. Suspicion soon falls on Emily's Cambridge tutor and also on another archeology enthusiast who was part of the group gathered the weekend before she disappeared—Ruth's friend Cathbad. As they investigate, Nelson and his team uncover a tangled web of relationships within the archaeology group and look for a link between them and the café where Emily's bones were found. Then, just when the team seem to be making progress, Cathbad disappears. The trail leads Ruth a to the Neolithic flint mines in Grimes 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?