In August 1940, Samuel Hartveld and his wife, Clara Meiboom, boarded the SS Exeter ocean liner in Lisbon, bound for New York. Aged 62, Hartveld, a successful Jewish art dealer, left a world behind. The couple had fled their home city of Antwerp not long before the Nazi invasion of Belgium in May 1940, parting with their 23-year-old son, Adelin, who had decided to join the resistance. Hartveld also said goodbye to a flourishing gallery in a fine art deco building in the Flemish capital, a rich library and more than 60 paintings. The couple survived the war, but Adelin...