Charlie asks Jim to investigate Raoul Barnaby, a medium who has gained the favour of Roberta Jardine. Charlie and Roberta's niece, the scheming Pauline, believe that Barnaby is a conman. Barnaby claims to have been contacted by the ghost of a 12 girl who was killed in an arson attack 20 years previously. Soon the child's grave is desecrated and a similar series of arson attacks occur.
Jim is charged with a new investigation into the arson attacks and uncovers a link between Roberta Jardine and Jack Plimont, the detective in charge of the case. It appears that Jardine's son was the arsonist and commited suicide by immolation over the unintended death of the girl. Plemont helped to cover up the truth.
Meanwhile Susan has sold the former home of the arsonist to Lil and finds ritual fire symbols in the attic.
At one of Barnaby's shows, Roberta calls Barnaby a liar. The next day Pauline reveals that she and Barnaby are partners and knew all about the fires. Pauline then pushes her aunt down the stairs. Pauline later turns up and Charlie's and tells Deborah that she killed Roberta in the fight. However Jim finds that Roberta survived the fall and has apparently committed suicide.
At the funeral, Plemont is horrified to see a figure dressed as a monk staring at him in the distance and point an accusing arm at him. Kim also sees this figure.
Later this figure appears at Plemont's window and lifts his/her hood. Plemont recoils in horror.
Jim uncovers evidence linking Pauline to Barnaby when he learns that Plemont has been found dead.
Barnaby meets Pauline on top of a cliff and feeling the heat (no pun intended) wants to leave Jersey. He also reveals to Pauline that he knows that she killed her aunt and made it look like a suicide. Pauline tells him to get a grip and they part ways. When Barnaby returns to his car, he finds himself locked in and overcome by the smell of petrol. He looks up to see the monk, who points at him in the same manner as was done to Plemont. The monk ignites the petrol and Barnaby dies as his car implodes. Pauline sees the monk through the smoke and flame.
Later that night, Susan visits Lil's house and encounters the monk herself. He chases her and she is saved by Jim's timely arrival. The beams from Jim's headlights illuminate the Monk's features and reveal a hideously scared face.
Jim correctly deduces that the Monk is Roberta's son and that he survived the suicide attempt. Roberta had him secretly flown out to a sanitorium in Switzerland.
Jim gets Barry to dress up as the Monk in order to trick Pauline into confessing her crimes.
Later Charlie asks Jim why he doesn't agree that the police were incompetent in preventing the monk from escaping back to the sanitorium. Jim says he finds it puzzling. Puzzling because the sanitorium are convinced that he never left…