In early 20th century Ireland, a sixteen year old youth Damien O'Laoghaire works on an archeological dig for the mysterious and magical "Claíomh Solais", one of the four artefacts of the mythical Tuatha De Danann. One night, his life changes forever when Damien and his younger brother Seosamh discover a magical sword known as “The Claíomh Solais”, earning them the respect of the mysterious English archeologist Eric Trent.

Damien travels with Eric to the National History Museum in Dublin to bring the sword there. Unknown to them, they have unintentionally attracted the interest of the legendary Fomorian King Bres who seeks to both destroy the sword and reconquer Ireland.

Damien and Eric have little choice but to seek out the Society of Saint Patrick, an organization of nationalist zealots who are skilled in fighting supernatural threats. Along the way, they are aided by both Simon Fitzgerald, an Anglo-Irish lord who has knowledge of Irish myths and Phil Rodgers, an eccentric British airman.

Both Simon and Phil work for the Anglo-American organization P. E.

C, a monster hunting army that also defends the human race from supernatural threats and who are willing to join forces with Ireland in the fight against Bres. .