Historical clue formulations

• "Mrs. Frisby and the Rats of ___" (Robert C. O'Brien children's book) — 2020-02-25
• "The Secret of ___" (1982 animated film) — 2012-08-07
• "The Secret of ___" (1982 film) — 2004-12-02
• "The Secret of ___" (1982 animated film) — 2004-07-01
• "The Secret of ___" (1982 film) — 2000-06-08