"The family was connected as neatly as characters in a detective story," Janet Morgan tells us on the first page of "Agatha Christie: A Biography." The line makes us hope that mysterious goings-on might follow.

Curtains. For on Page 2 we are presented with one of those intractable diagrams of family ancestry that always made us gag in school when the Yorkists and Lancastrians had to be sorted out and that ultimately tell us nothing suggesting the neat connections of a detective story.

Agatha Christie did it with mirrors; Janet Morgan does it with minutiae. She certainly does not commit the sin of overinterpretation: She presents "facts" (perhaps forgetting they can be as slippery as fiction). But must we have all of them? Must we learn every detail of the decor of Agatha and Archie Christie's flat at Addison Mansions? Or of the countless houses in her marriages to Christie and Max Mallowan? We should be thankful that Laura Ashley wasn't around back then or we'd be following the tracery of every sprig in the wallpaper, the matching curtains, the sheets.

This is the difficulty that lies at the heart of Morgan's biography: we never get to know Agatha Christie. Biographers are not expected to be clairvoyant; however, Morgan was chosen by Christie's daughter, given access to papers, notebooks and a mind-boggling number of Christie's acquaintances. So she certainly had her sources. Yet the choice of Morgan is strange. She has written one other book: "The House of Lords and the Labour Government," and edited others having to do with politics and broadcasting. And this is the "authorized biography" of a mystery writer who, in terms of sales, is right up there with Shakespeare and the Bible.

The plethora of detail somehow suggests that Agatha Christie's life was just the one Morgan presents. Of course there were unhappy episodes: her father's death seems to be noted as traumatic, but then forgotten; and Archie falls in love with Nancy Neele, triggering (perhaps) the famous "disappearance." Aside from that, though, hers appears to be a life of seamless satin. Happy childhood, happy adolescence, happy marriages (yes -- even the one to Archie) and certainly a career that would strike any beginning writer today as enviable.

That career began with "The Mysterious Affair at Styles"; the manuscript rested with the Bodley Head for two years, and Agatha "forgot about it." Her early attitude toward writing seemed to be that it was a lark. But later her professionalism and hard-headedness became clear. Agatha might have been "shy," but she was nobody's fool.

But the reader is probably not ravenous for the facts surrounding the publication of every book, the producton of every play.

To dilute the real genesis of Christie's material in this way is sad. Readers want to know where any writer gets his ideas -- all the more so with one as brilliant at plotting as Agatha Christie. She left behind more than 30 "plotting books" that "show Agatha's mind at work, taking up an idea, playing with it . . . turning it inside out . . . It illuminates the way in which Agatha settled on an idea, proceeding from the first inkling to the concept." Morgan gives us one lengthy example from these notebooks. She says it would be "tempting" to explore them, but that "this . . . is not the place to explain the genesis of every plot and every story." And this attempt is made only after 300 pages. If Agatha Christie's biography is "not the place" to do this, where is it?

Where Morgan comes across well is in her account of the famous 10-day disappearance. It is here that one devours her facts. I am not quite certain, though, why she finds the interpretations of the press "lunatic," since Chapters 10 through 12 have room to spare for several speculative books on Christie's disappearance.

Morgan's reconstruction of the events surrounding those 10 days is plausible; she bases it largely on Christie's telling a psychiatrist later as much as she could remember, and apparently she wanted desperately to remember. Yet one still wonders about the hundreds of pounds in her money belt, her calling herself "Mrs. Neele" and her having told her sister previously, "I could disappear if I wished and set about it carefully."

Janet Morgan's account of Agatha Christie's writing is both appreciative and objective: "She produced a succession of dazzlingly cunning plots, whose elucidation was the sole purpose of each book. Unlike other detective-story writers, she was not stylistically ambitious: her prose is pedestrian but undistracting. She did not seek to capture the reader's sympathy for one character or another."

Neither does Janet Morgan. One only wishes she'd fallen prey to the temptation to do more with those "plotting books," or to forget, perhaps, about preserving an Institution.