The affair of the balcony ended, if indeed it ever began, with the appearance in July of a slender book of curious title, obtainable in very few places, one of them being an art gallery in a frosted storefront on Broadway near Franklin Street.

Called ''The B-Thing'' and produced by four Vienna-based artists known collectively as Gelatin, the book is demure to the point of being oblique. What little explanation it contains appears to have been scribbled in ballpoint. Among the photos and schematic drawings, there are doodles of tarantulas with human heads.

In short, the book belies the extravagance of the feat it seems to document: the covert installation, and brief use, of a balcony on the 91st floor of the World Trade Center, 1,100 feet above the earth. Eight photographs -- some grainy, all taken from a great distance -- depict one tower's vast eastern facade, marred by a tiny molelike growth: a lone figure dressed in a white jacket, standing in a lectern-size box.

The contemporary art world, of course, is rife with acts of subversion followed by boasting, which is known as ''documentation.'' In that context, the beauty of the balcony was that it so literally pushed the envelope. Yet since that Sunday morning in March 2000, when the balcony was allegedly installed and, 19 minutes later, dismantled, the affair has taken on the outlines of an urban myth, mutated by rumors and denials among the downtown cognoscenti.