The man who was Thursday: A Nightmare (Headline Review Classics) (libro en inglés) - G.K. Chesterton

A group of anarchists are under surveillance by Scotland Yard in Chesterton's hugely popular metaphysical thriller. The Supreme Anarchists Council is dedicated to overthrowing the world order. To keep their identities a secret, each of them has been named a day of the week. Gabriel Syme, an eccentric poet, is recruited by Scotland Yard to infiltrate the group. He tracks down the six men and manages to win a place on the council. But in a bizarre and surreal twist of events, Syme realises that five of the six members are not at all what they seem...