A pilgrim's journey to Santiago de Compostela turns deadly when a murder in Le Puy-en-Velay draws Lord Francis Powerscourt into a dangerous investigation. Powerscourt must navigate a series of escalating murders targeting pilgrims along the ancient route, facing threats that endanger his own life. The investigation culminates on the day of the Bull Run at Pamplona, where Powerscourt must unmask the killer before becoming the next victim.

The premise sets up a classic historical mystery, likely appealing to readers who enjoy period settings and intricate plots. The inclusion of specific historical locations and events, such as the Camino de Santiago and the Pamplona Bull Run, suggests a focus on atmospheric detail and historical accuracy. The narrative structure, centered on Lord Powerscourt's investigation, points towards a character-driven suspense story with a clear objective for the protagonist. The escalating danger and the race against time indicate a pacing designed to maintain reader engagement throughout the unfolding mystery.