Archeologist David Hyden is hell-bent to disprove his Biblical archeologist father’s religious theories. After his father is found dead at the center of Stonehenge with a strange glowing spiral engraved into his palm, David decides to challenge his father’s theory that Maeshowe—a passage grave ruin in Stenness, Scotland—possesses metaphysical powers. However, the morning after his arrival in Stenness, David wakes to find everyone else in town is dead.
NATO pathologist Brynne Thatcher is trained to recognize the subtle features of subsonic death, a unique forte and her only leg-up in a career dominated by men. Sound is the ideal weapon: an indiscriminate killer that leaves almost no trace upon its victims. She is testing an acoustic cannon in the grasslands a short distance from Stenness. Thatcher is certain her weapon caused the Stenness massacre, but all bets are off when she pinpoints Maeshowe as the source of deadly noise. The ruin erupts with low-frequency sound every 77 hours. Each explosion is larger and deadlier than the last. The only clues to stopping Maeshowe are the spiral petroglyph glowing inside its central chamber and the lone survivor, David.
Investigating the connection between the two glowing spiral symbols, Thatcher and David uncover Brenton’s most bizarre theory: There are four locks and four keys lost throughout antiquity. Any man who finds a matching lock and key will gain one of the powers of the Four Horsemen of Apocalypse (Conqueror, War, Plague, and Death). Displacement of a key awakened the passage grave. Unless the “key” is placed into the petroglyph “lock,” the ruin will kill every living thing.
Finding the key won’t be easy. A clandestine brotherhood known as the Abaddon is sworn to protect the keys. As Maeshowe’s eruption spreads across northern Europe, the leadership of the Abaddon crumbles. A new leader of the dark society seeks to become Conqueror, and a race to the Apocalypse begins.