This is Jan Muller's Horseman.

In 1933 his family fled the Nazis to Prague, and later to Bex-les-Bains, Switzerland; there he experienced the first of several attacks of rheumatic fever. He visited Paris in 1938 and two years later was apprehended and interned in a camp near Lyon. Shortly after the fall of Paris, Müller was released, at which time he moved to Ornaisons, near Narbonne. Following an unsuccessful attempt to escape to the United States from Marseille, he was able to cross the border into Spain in 1941 and proceed via Portugal to New York.   - Julie Heller