On a Connecticut farm, James Mayo's two sons both love Ruth Atkins. Robert, the younger son, is sickly and dreams of escaping to a romantic life somewhere "beyond the horizon." Andy is hard-working and steadfast and loves his brother deeply. When Ruth reveals that she loves Robert and not, as everyone believed, Andy, Robert's plans to go to sea with his uncle are disrupted. He decides to stay at home and marry Ruth, while Andy, unwilling to remain close at hand as his brother marries the girl he loves, takes Robert's place on the voyage. This turn of events leads to heartache and tragedy for everyone involved.
During World War I, a German U-boat sinks a British ship and takes the survivors on board. After it takes a wrong turn, the submarine takes them to the unknown land of Caprona, where they find dinosaurs and neanderthals.
In Montauban in 1944, Julien Dandieu in a surgeon in the local hospital. Frightened by the German army entering Montauban, he asks his friend Francois to drive his wife and his daughter in the back country village where Julien has an old castle.