Young newlyweds Peter and Dorothy Muilenburg found their way from New Hampshire to the Virgin Islands. He had been a civil rights Freedom Fighter, jailed in Mississippi while protesting racial injustice. In St. John, she founded the Pine Peace School. They both taught. On an East End beach, he built a sailboat strong enough to take them anywhere, and they put to sea with their two young sons. But their crew was not yet complete. Santos, a schipperke, came to them as a tiny puppy and sailed with them all his life—75,000 deep-sea miles—four times across the Atlantic, crisscrossing the...