PC Rowan responses to an anonymous emergency call and find archaeologist Professor Brigstocke dead in his library and the house broken into. The professor was said to hide a treasure and Greengrass decides to find it. Clues lead to the ruins of Saint Columba's Abbey on the Ashfordly estate. But also Mary Secker, who is writing a book on 12th century monasteries, is interested in the ruins. Lord Ashfordly is hosting a fishing party and is not pleased to find fishing net and no fish in his river. Blaketon suspects Greengrass is behind it and when the old scoundrel enters the abbey to look for the treasure, Blaketon is close behind him. They both get trapped and Blaketon breaks a leg when part of the ruins cave in, and Greengrass lights a fire to keep him warm.