At the foot of Glastonbury Tor is a blessed spring where the water runs red, supposedly representing the blood of Christ. But when Gwyneth and Hereward's friend, Brother Timothy, visits the spring one day, the water is running red for another reason - a travelling merchant has been killed there! Gwyneth and Hereward set about trying to solve the murder and once again find themselves calling upon the old hermit, Ursus, for help.