Mathieu Galmier, formerly of the Pasteur Institute, has to leave Paris under a cloud when one of his pioneering experiments in hematology goes awry. He is given refuge—of sorts—in London by Sir Juliam Templeforth. Unfortunately, the rewards both men hope to reap from continuing the experiments are slow to materialize. The research hits snags, and its human costs are beginning to weigh on Mathieu's conscience.

Complicating matters further, some of Sir Julian's unruly Irish tenants have come to London to demand satisfaction, and Mathieu's presence has been detected by Philippe and Myrtille de Valcoeur, who have an intense interest in his research—seemingly more mystical than scientific.

When complications lead to catastrophe, Mathieu has to flee. But his past proves exceedingly difficult to escape . . .