In 1971, a British folk singer named Steve Tilston gave an interview to ZigZag — a small, underground-rock rag named for a Captain Beefheart jam and a popular brand of rolling papers — in support of his debut LP, a collection of earnest, fingerpicked guitar songs that recall Nick Drake and Jackson C. Frank. When asked if he thought fame and fortune might prove toxic to his songwriting, Mr. Tilston did not equivocate. “Yes, yes, of course it will,” he recalls saying. “My heart will suffer.”

John Lennon — then 30 and about to release “Imagine” — read Mr. Tilston’s interview, was stirred by his conviction and scribbled him a letter saying money didn’t change anything. Or not really. “So whadya think of that,” it ends.

Image John Lennon Credit... Associated Press

Mr. Tilston was never able to answer. The note was sent to him care of ZigZag and lost for 34 years — perhaps nabbed at the time by an employee of the magazine who recognized its potential value to collectors. Mr. Tilston didn’t find out the correspondence even existed until 2005, when a man approached him to authenticate it, and Mr. Tilston slowly realized what had transpired. “I emailed him and said, ‘Look, you can have the letter, but I’d really like to know what it means, what it says,’ ” Mr. Tilston said. He described Lennon’s tone (only slightly wistfully) as “very brotherly.”