It was 7 a.m. on Sunday when the single phone at the bottom of the stairs echoed through my parents’ red-brick house, right off Monticello Park in Fort Worth. “Mr. Gregory,” a woman said as my father picked up, “I need your help.” Who are you? he asked in his Texas-Russian accent, still half-asleep.

The caller said only that she had been a student in his Russian language course at our local library, and that he knew her son. In that instant, my father, Pete Gregory, linked the voice to a nurse who sat in the back of his class and had once identified herself as “Oswald.” Until this phone call, he hadn’t realized that she was the mother of Lee Harvey Oswald, a Marine who had defected to the Soviet Union only to return two and a half years later with a Russian wife and a 4-month-old daughter. My father helped Lee and his young family get settled in Fort Worth a year earlier. The Oswalds had been my friends.

My father now understood that the woman on the other end of the line, Marguerite Oswald, must have taken his class to communicate with her daughter-in-law, Marina, who spoke little English. It was also clear why she needed his help. Two days earlier, Marguerite’s son shot the president of the United States. While Lee Harvey Oswald was sitting in a Dallas jail cell, his wife and mother and two young daughters were hiding out at the Executive Inn, a commuter hotel near the airport, where they were taken and then abandoned by a team of Life magazine staff members. Marina Oswald had become the most wanted witness in America. She needed a translator fast.

Hours after the Kennedy assassination, my parents and I experienced the shared horror of realizing that the Lee Oswald we knew, the one who had been in our house and sat at our dinner table, was the same man who had just been accused of killing the president. The Secret Service first knocked on my parents’ door at 3 a.m. on the morning of Nov. 23, 1963. The following day, just 45 minutes after my father hung up with Marguerite, an agent named Mike Howard picked him up and drove him to a Howard Johnson’s on the Fort Worth-Dallas Turnpike, where they met Robert Oswald, Lee’s brother. As the family’s translator of choice, my father was now part of the plan to get the Oswald women out of the dingy hotel room and into a safe house that Robert had arranged at his in-law’s farm, north of the city, so Marina could be questioned....