summary She tells us the story of Mr Plattner, a professor at an English private school, whose banal life only comes alive when he discovers an interest in chemistry. It is fun to analyze in a very empirical way the samples that bring him his students. Until the day when one of them brings him a strange green powder ... The combustion of the latter leads to an explosion during which Plattner literally volatilizes; There is no trace of him. He reappears 9 days later, alive, with a very strange story. He tells us that he spent all this time in a parallel world, a very obscure overseas world lit only by a phosphorescent light of green color and peopled with specters of the same color. These ectoplasms are none other than the "spectators of the overseas," the souls of the deceased obliged to look down on the consequences of the actions realized during their lifetime. Finally, after nine days of wandering, and seeing the shadow of death, Plattner accidentally regains our world.