In 1881, he was sent to Argentina, where an Irish immigrant population needed English-speaking priests. Outside of Buenos Aires, it was a scattered population. Stone sometimes rode 40-50 miles on sick calls. He caught black smallpox while helping the sick in Buenos Aires. Both in the United States and in South America, he served as provincial (regional leader of a religious community). He also started foundations in Chile and Brazil.
Through the years, he never forgot his children. While they knew about him, however, there was no contact. But after reading his last book, published in 1920, his daughter Frances decided to visit him. By then, Stone's two surviving daughters were in their late 50s, one a widow. When they finally reunited, a biographer notes, "it had been years since he wept."
He ended his days in their company, celebrating daily Mass at Frances' California home. In 1921, at 81, he passed away at the house. Passionist historian Roger Mercurio comments:
Fr. Fidelis of the Cross had made this supreme sacrifice to become a missionary of the passion. Unfortunately his sacrifice also meant a sacrifice for his children. Both he and his daughters were granted a foretaste of peace in those final weeks in San Mateo.
Perhaps Passionist scholar and archivist Robert Carbonneau best sums up Stone's journey when he writes, "What an exciting life!"