Ceridwyn Brent and her boss, Cheryl Tennant, are on a mission. Prove their thaumic power generation system works, provide almost limitless, clean electricity for Great Britain and the rest of the world, and maybe sort out their slightly overcomplicated private lives. The first trial of the generator is to take place at Stonehenge, a Neolithic monument built five thousand years ago during a spike in magical activity, though no one really knows why. Uncovering the secret of why the great henge was built uncovers a secret about Ceri and why she is a sorceress. Unfortunately, their private lives are not getting any less entangled any time soon. 

But as Ceri tries to deal with the knowledge she has gained, and cope with giving a lecture at a prestigious academic conference, an old adversary returns, determined to destroy her. As the bodies start to pile up and no one seems able to find the murderer, Ceri and Lily, her half-succubus lover, must go out on their own and seek help from their sworn enemies in order to fight back. 

Amidst the chaos and death, Ceri must still seek out and unlock the secret of the dragons and their blood. Her future could depend upon it.