This book details the experiences of Théodore Flournoy (1854-1920), professor of psychology at the University of Geneva, during the five years he spent attending the seances of Hélène Smith, a pseudonym for Catherine Müller (1861-1929). Smith was a medium who received spiritual messages through visual and auditory means as well as raps on the table from her spirit guide and protector named Leopold. Flournoy studied Smith and wrote of the different cycles she inhabited as she claimed to be the reincarnation of Simandini the daughter of an Arab sheik, the favourite wife of a Hindu prince, as well as a reincarnation of Marie Antoinette. She also claimed to have contact with people living on Mars and to be able to speak their language which she wrote down during her seances, as well as sketches of the landscape she witnessed (see image below).

February 16, 1896. – The idea of a special handwriting belonging to the planet Mars occurs for the first time to Hélène's astonishment in a Martian semi-trance.

August 22. – Hélène for the first time writes in Martian. After various non-Martian visions Mlle. Smith turns away from the window (it rained hard, and the sky was very gray), and exclaims 'Oh, look, it is all red! Is it already time to go to bed? M. Lemaître, are you there? Do you see how red it is? I see Astané, who is there in that red; I only see his head and the ends of his fingers; he has no robe, and here is the other (Esenale) with him. They both have some letters at the ends of their fingers on a bit of paper. Quick, give me some paper!' A blank sheet and the pocket-pen are handed to her, which latter she disdainfully throws down. She accepts an ordinary pencil, which she holds in her customary fashion, between her middle and index-finger, then writes from left to right the three first lines of Fig. 21, looking attentively towards the window at her fictitious model before tracing each letter, and adding certain oral notes, according to which there are some words which she sees written in black characters on the three papers — or, more correctly, on three white wands, a sort of narrow cylinder, somewhat flattened out — which Astané, Esenale, and a third personage whose name she does not know but whose description corresponds with that of Pouzé, hold in their right hands.