CAUGHT IN THE PULL OF THE MANDRAGORA HELIX, a spiral of pure energy with a controlling intelligence at its centre, the TARDIS makes a forced landing in Northern Italy in 1492. The Doctor makes a forced landing in Northern Italy in 1492. In San Martino, the old duke has been poisoned by his brother Count Federico with the assistance of the court astrologer Hieronymous. Federico and Hieronymous now plot the death of Prince Giuliano, heir to the dukedom.
While the Doctor discovers that a portion of Mandragora energy has travelled to San Martino in the TARDIS, his companion Sarah Jane Smith is kidnapped by adherents of the Cult of Demnos, an ancient religious sect that worships the god of the twin realms of moontide and solstice. Narrowly escaping a beheading at the hands of the Count’s executioner, the Doctor discovers the temple of Demnos, hidden in catacombs beneath the city. He rescues Sarah before she can be sacrificed by Hieronymous, the secret leader of the cult.