Historian Dr. Nina Gould is visited by her stepbrother, whom she had not seen for ages. With him, he brings a man holding him hostage. Nina has to help them locate a man reputed to own the Holy Grail, or else her stepbrother would be implicated in a serial killing spree. 

Her research on the Grail reveals that a unit of Allied soldiers, called the Perceval Chapter, were entrusted with the Grail during the North African Campaign in 1944, tasked to keep it out of Nazi hands.

Because of this information, she subsequently joins up with investigative journalist Sam Cleave, who has been hired by retired police inspector Peter Carroll to track down the man responsible for the string of child murders. When they compare notes, they uncover a dire secret among the elite soldiers of the Perceval Chapter, and the reason the Holy Grail disappeared without a trace after World War II.

When Edinburgh explorer and billionaire David Purdue invites the wrong people to admire his private relic collection, he is attacked and left with a wound that refuses to heal. His condition rapidly deteriorates and eventually, Nina’s skepticism in the existence of holiness is tested when she has to decide if she will take a leap of faith to save the life of her friend by using the Holy Grail’s power.