For years, Alfred Ludens has pursued mathematician and philosopher Marcus Vallar in the belief that he possesses a profound metaphysical formula, a missing link of great significance to mankind. Luden's friends are more sceptical. Jack Sheerwater, painter, thinks Marcus is crazy. Gildas herne, ex-preist, thinks he is evil. Patrick Fenman, poet, is dying because he thinks Marcus has cursed him.

Marcus has disappeared and must be found. But he is a genius, a hero struggling at the bounds of human knowledge. Is he seeking God, or is he just another victim of the Holocaust, which casts its shadow upon him and upon Ludens, both of them Jewish? Can human thinking discover the foundations of human consciousness? Iris Murdoch's endlessly inventive imagination has touched a fundamental question of our time.