Plus was born in Boulogne-sur-Mer, France, where he attended the Jesuit collge. In 1899 he entered the Jesuit novitiate in Amiens and was ordained there. Because of laws that persecuted religious orders at that time, Fr. Plus had to leave France in 1901 and did not return from this exile for ten years, during which time he studied literature, philosophy, and theology in Belgium and Holland. He also taught courses in the field of humanities. At the advent of World War I, Fr. Plus enlisted as a soldier, and subsequently as a chaplain. It was during this time the he began to write.