Madeleine Stern, who died Saturday at 95, was a leading Manhattan rare-book dealer and one-half of a team of literary sleuths that discovered the secret “blood-and-thunder” writings of Louisa May Alcott.

Stern was the author of more than 30 books on feminists and American history. She and her business and life partner of more than a half-century, Leona Rostenberg, operated Rostenberg and Stern Rare Books from their Upper East Side apartment.

Acting on a tip from another Alcott scholar in the early 1940s, the pair jointly uncovered evidence that the revered author of “Little Women” had an earlier career writing racier books that featured drugs, transvestitism, and murder. Although the secret was disclosed in Stern’s 1950 biography of Alcott, it did not become general knowledge until Stern published “Behind a Mask: The Unknown Thrillers of Louisa May Alcott” (1975).

In addition to monographs on several other authors and on the rare books trade, Stern published volumes of memoirs written with Rostenberg, who died in 2005 at 96. The last of these was “Bookends: Two Women, One Enduring Friendship.”

The pair always insisted that they shared a deep spiritual bond, but that their relationship did not have a sexual component. They occasionally referred to each other as “Watson and Holmes” and were photographed in deerstalkers, wielding magnifying glasses.

Their partnership dated from the 1930s, when they were undergraduates in Manhattan. In 1944, Stern backed Rostenberg’s entry into the book trade, and after World War II, the pair traveled to Europe to buy books from dealers. They later became founders and mainstays of the Antiquarian Book Fair in New York.

A play based on their lives, “Bookends,” is currently running at the New Jersey Repertory Company in Long Branch, N.J.