The White Flag AA meeting — "one longtime member of the White…"
one longtime member of the White Flag Group is a prognathous lady named Louise B. who tried to take a map-eliminating dive off the old Hancock Building downtown in B.S. ’81 but got caught in the gust of a rising thermal only six flights off the roof and got blown cartwheeling back up and in through the smoked-glass window of an arbitrage firm’s suite on the thirty-fourth floor
Context
The idiom compounds into an adjective: Louise B.'s "map-eliminating dive," metro Boston AA's house myth of willed self-annihilation cancelled by a thermal. She survives her own map-elimination and lands rabidly Christian on an arbitrage firm's conference table — the one person in the book who jumps off the jumping-off place and gets blown back up.