A bizarre road accident propels Celcius Daly into an investigation that will reveal the truth about his mother's death thirty years ago.

Father Aloysius Walsh spent the last years of his life painstakingly collecting evidence of murder: an unsolved killing spree of unparalleled savagery that blighted Ireland's borderlands at the end of the 1970s. Pinned to his bedroom wall, a macabre map charts the grim territory of death: victims, weapons, wounds, dates – and somehow, amid the forest of pins and notes, he had discerned a pattern...

So why did Father Walsh deliberately drive off the road to his death? Why, when Inspector Celcius Daly arrives at the scene, does he find Special Branch already there? And why is his mother's name on the priest's map?