A simple job turns deadly when Mary Wandwalker, novice detective, is hired to chaperone a young American, Rhiannon, to the Oxford University Summer School on the ancient Celts. Worried by a rhetoric of blood sacrifice, Mary and her operatives, Caroline, and Anna, attend a sacrifice at a sacred well. They discover that those who fail to individuate their gods become possessed by them.

For the so-called Reborn Celts, who run the summer school, have been infiltrated by white supremacists. Could their immersion in myth be less a symbol for psychic wholeness and more a clue of their intent to engage in terrorist violence? Who better to penetrate their secret rites than an apparently harmless woman of a certain age?

Mary agrees to spy on the Reborn Celts, then learns, to her horror, of Anna's passionate affair with the chief suspect, Joe Griffith. With Griffith also the object of Rhiannon's obsession, Mary realizes too late that that these 21st century Celts mean murder.

The Reborn Celts draw Mary and her friends into three rites to summon their gods: at an Oxford sacred well, by the Thames on the way to London, and in Celtic London, where bloodshed will restore one of the Thames' 'lost rivers.'

Before the fatal night of the summer solstice, Caroline and Anna race to London seeking Mary, who has been kidnapped. Will she end as the crone sacrifice? Or will the three women re-make their detecting family, so re-constituting a pattern of archetypal feminine compassion?