Sanderson sailed back to Swatow in 1946 expecting to resume the work she had left in 1937. For the first two years, she did. Her 1948 “Dear Friends” letter describes a school recovering its rhythm, twenty-two students accepting Christ that term, the women’s group meeting again every week, classes back in session in the buildings she had helped raise more than two decades before. After nine years of war and absence, the school was recognizable as the one she had left. By the time she wrote the next batch of letters home, that would no longer be true.
The People’s Republic was declared on October 1, 1949. Seventeen days later Sanderson sat at her desk at the American Baptist Mission in Swatow and wrote a long letter to Mrs. Charles K. Sears in New York, watching troops move through Kakchieh and the new regime’s posters appear on the church walls. By early 1950, books her American supporters had mailed her in Swatow were no longer arriving, the first sign that someone was reading her mail before she did. That spring, the school she had run for thirteen years was merged with the boys’ academy at Kakchieh under a new name, Kak Kuang Middle School. In May she wrote her sister Clara that the new authorities seemed inclined to let her continue, and that the school had taken on an unmistakably new register. “New thoughts, new movements, new outlooks are in the air,” she wrote. She hoped to find some part of the change worth participating in. She also acknowledged that certain old realities remained. She was working inside a system that was steadily closing around her, finding optimism in each new constraint.
In January 1951 the Colby Alumni Office sent her a routine biographical update form. Where it asked for the dates of her missionary service, she filled in 1918 and a question mark. Three months later, on the morning of April 9, 1951, the Chinese Communist police came to her door at Kakchieh. The charge was spying for the American government. They led her to a room inside her own house and held her there for four months. The few classes she had still been teaching ended. The few students who had still been attending were sent home.
In August 1951 she was taken across Swatow Bay by boat to a former Catholic mission building and placed in solitary confinement. Three other missionaries, two men and one woman, were held in separate rooms in the same building. She did not see them, except once a day through a small barred opening in her door when guards led them past her cell to a single shared toilet. Through seventeen months in that room, the only printed materials she was allowed to keep were two Bibles, a New Testament, a small devotional book called God’s Answer, a French dictionary, and a two-volume copy of Thackeray’s Pendennis. The single piece of mail that reached her in those seventeen months was a four-page July 1951 issue of the Colby College Bulletin, which she would later say she read item by item, many times over. She memorized passages of scripture. She improved her French. She relearned the technique of finding square root by hand, working backward through the process, and tried unsuccessfully to derive cube root the same way. Pendennis, by her own count, she read through about ten times.
She was released without explanation on the last day of December 1952. Guards took her and her three fellow prisoners by boat to the Swatow customs house, separated her from the other woman at bayonet point, and put her on a vessel for Hong Kong. The two men were sent back to their cells. Five days later they too were released and put on a boat for Hong Kong. Within two months Sanderson was home in South Berwick, Maine. She would not speak publicly about the twenty-one months for over a year.
When she finally did speak, three accounts of her detention emerged in three very different voices, each louder than the last. The first was her own December 14, 1953 letter to Mr. Dyer at the Colby Alumni Office, which carefully listed the printed materials she had been allowed in the cell and described what she had done with the time. It contains the most personal sentence she ever wrote about those months: “Perhaps some day I can tell more about it.” She did not tell more, at least not in writing. The second voice belonged to a 1960 Maine newspaper feature that ran across two columns under a headline she would never have used herself: “Continues Her Work After Imprisonment By Communists.” The reporter described the solitary confinement in dramatic terms, foregrounded the Cold War framing, and gave her detention the public meaning the era required. The third voice was Colby College’s 1965 honorary Doctor of Divinity citation, which named her years of confinement evidence of Christian fortitude in the living of her convictions. All three accounts were factually true. But Sanderson’s own voice was the quietest of the three, and over the decades that followed, it was the one most often replaced by the louder ones. Other people made her detention a story of fortitude. She did not.