On a recent Saturday afternoon, the group's events committee convened at Shakespeare & Co., a bookstore on upper Broadway where the committee plans a public party in May to draw attention to the books. Part of the society's agenda, directed largely from the national headquarters in Mankato, is to rekindle interest in the books. They have succeeded to a degree, with HarperCollins reissuing four of them to date (others are to follow soon), and there is even talk of a Betsy-Tacy cable television series.

The society's sistren, to borrow Betsy's term, say they stop short of listing their membership on their resumes. But they advertise it in other ways. Ms. Martin wears a big white button on her coat that proclaims, "I Betsy-Tacy." When people ask her what it means, "I explain, and there's either a dumbfounded silence, or they say 'Is it like the Bobbsey Twins?' "

Like any fascination, this can border on obsession. One member joined from upstate New York, and, on her first wedding anniversary, told her husband that what she really wanted was to attend a Betsy-Tacy Society meeting. He complied, driving for hours to Brooklyn.

"He was really sweet and supportive of this rather strange request," recalled Linda Duchin, a Manhattan film distributor who first happened upon the books at 30 and is now the society's vice president.

Another husband, Ms. Duchin said, announced that he wanted to have his wife "deprogrammed" after she left a sticker on his pillow that declared, "I'd Rather Be Reading Betsy-Tacy." THE WOLFEPACK

"Forget it." I patted his arm. "I mean forget the murder. Let Nero Wolfe do the worrying, I always do. Did you elect your four new members this morning?"

Rex Stout, "Too Many Cooks"

Even for a book group preoccupied with murder, New York can be a scary place. Just ask the members of the Wolfepack, founded in 1979 by fans of Nero Wolfe, the obese, gourmet-chef-employing, orchid-tending, yellow-silk-pajama-wearing New York private eye hero of 35 mysteries by Rex Stout.

Eager to attract new members a couple of years ago, the group wrote up a personal ad and placed it in The Village Voice. "Single white male," they began, and filled in the rest of the details ("Weighs a seventh of a ton") in a way they thought would send a clear signal to other Nero Wolfe readers, and no one but other Nero Wolfe readers.

Of course, it backfired.

"We got people writing in their bizarre sexual fantasies, some of them involving yards and yards of yellow silk," said Ellen E. Krieger, an editorial director at a publishing house and the group's original and only "werowance," or supreme leader.

"We suddenly realized there were some really sad and lonely people out there, who would respond to such an ad," said Ettagale Blauer, another member. "We didn't know whether to tell them the truth or not."

The group also has blood on its hands -- restaurant blood. Every year, the Wolfepack holds a dinner at a Manhattan restaurant, and every year the restaurant has gone out of business, Ms. Krieger said.

But other than that, the Wolfepack seems to be a fairly self-contained society, devoted to its hero, invariably referred to as "Mr. Wolfe," and his sidekick and Boswell, Archie Goodwin. Every spring there is a shad roe dinner, because shad roe was featured in one of the books. A popular activity is casting the perfect Nero Wolfe movie. (The group wasn't totally happy with the television series, starring William Conrad, that barely lasted a season in the early 80's.) The members use terms from the books as their computer passwords at work, and feel sad about the fate of the former Yugoslavia (Mr. Wolfe was from Montenegro). Last year they made a pilgrimage to Brewster, N.Y., to see Rex Stout's home. (He died in 1974.)

"They got Rex's typewriter out of the garage or wherever it was and showed it to us," another member, Marvin Kaye, said only a little reverently.

The Wolfepack has 350 members around the world, but 100 in the city -- the single largest concentration anywhere. Members pay $25 a year.

Through what they call "the corpus," they visit a New York that has either disappeared or never was.

"Archie can park the car almost anywhere," said Mary Glascock, a 10-year veteran. "Their mail is delivered on time," Ms. Krieger noted.