The high-risk exploration of secret Celtic chambers beneath the Roman Baths unlocks an ancient love story. Gillian and Ben unravel the tragic tale of Celtic warrior queen Boudicca and Roman soldier Quintanus, while confronting their own past relationship amid the dark and claustrophic chambers.

A British First World War tank containing the burnt remains of six bodies is uncovered in France. Evidence of a war crime soon emerges and Gillian inadvertently ignites an international feud with French and German archaeologists. But when violent events occur at the dig site, it becomes clear someone is trying to cover up the truth.