Not so much an untold story, but an untold thing: The Massachusetts Body of Liberties (1641). It listed out 100 liberties and rights that the people in the Massachusetts Bay Colony had at the time, in order to guide the General Court (Which, fun fact, is the direct descendant of the MA state legistlature!). What makes this document interesting is that it contained 16 of the 26 rights found in the Bill of Rights, and it was the first document protecting them, in both American and English law. It set a legal precident in the MA and the US, and infludenced the Bill of Rights. It was, for the most part, ahead of its time, and I think it should be found in more books!

Sources: http://www.mass.gov/anf/research-and-tech/legal-and-legislative-resources/body-of-liberties.html The State Constitutional Pedigree of the U.S. Bill of Rights (Donald Lutz)