Based on the lives of Albert and Thyra Johnston, who lived in New Hampshire in the 1930s and '40s.
Dr. Carter is shown traveling by U.S. Coast Guard boat from Portsmouth N.H. to the Isle of Shoals, about 6 nautical miles from the city harbor. However, when the boat arrives to its destination it is actually the Cape Neddick Lighthouse station (a.k.a. the Nubble) just off the coast from York, ME. The house the doctor is shown entering is the lighthouse keeper's residence.