IN 1885, when the Metropolitan Museum of Art was young and New York was home to much new wealth but only a few old masters, the museum showcased a painting on loan from Europe that created a minor stir.

It was a small wood-panel Pietà depicting an earthy-looking Virgin Mary holding her dead son, assisted by two muscular angels, a tableau widely acknowledged to have been created by Michelangelo, though the Met’s catalog went only as far as saying that the painting had been attributed to him by its owner.

That owner was a German baroness who had sent the painting to America in the hopes of selling it. But it never found a buyer and eventually passed into the hands of acquaintances, members of an upper-middle-class Rochester family who hung it for many years above a fireplace, referring to it with great affection — but little direct evidence — as “the Mike.” After it tumbled from its perch while being dusted one day in the 1970s, the painting was moved from the mantel to a safe spot behind the couch, where it effectively disappeared from awareness, both scholarly and otherwise.

The kind of work the family believed it to be — an easel painting by Michelangelo — is among the most elusive treasures in Renaissance art. Michelangelo probably made only a handful, is not known to have signed any, and broad consensus has formed around the attribution of only one, at the Uffizi Gallery in Florence. Tonawanda, N.Y., a faded mill town north of Buffalo, might be the last place on earth scholars would begin the hunt for another. But over the last decade, thanks almost entirely to the stubborn crusading of a retired fighter pilot there named Martin Kober, who inherited the Pietà, the painting has re-emerged as the main character in a compelling art-historical mystery.