Tony and Carol investigate when a 500-year-old skeleton in unearthed while foundations are being excavated for a hotel extension. However, underneath the body, they find two more modern corpses. And when a journalist vanishes, and the hotel is burnt to the ground, Tony suspects the suspect may be obsessed with Joan of Arc and killing imagined heretics.

Bradfield is in panic as someone preys on its most vulnerable—its hospital patients. Carol must juggle how to warn the public, and how to keep a predatory MI5 official at bay. The only way out is to solve the case fast—but there is very little to go on, even for Tony.