From ghoulies and ghosties and long-legged beasties and things that go bump in the night, Good Lord, deliver us! Of course. But from well-meaning neighbors who drop in from time to time to see how things are going when a baby's on the way? What could be more reassuring?

In Fay Weldon's latest novel, a lot. That is, since the reader knows what the pregnant heroine, Liffey Lee-Fox, only senses: that drab, horsey Mabs Pierce, who lives with her husband Tucker and their five children in a nearby farmhouse, is not the "smiling, friendly countrywoman with a motherly air" she makes herself out to be. Mabs, in fact, is a witch.

"Puffball," however, is no mere genre exercise in occult obstetrics; instead, it is a sly comedy that dallies in the shadows before moving triumphantly into the light. What looks like certain maleficence -- Mabs' obsessive attempts to dose Liffey secretly with one harmful herbal potion after another, for example -- never really comes to pass. Each time it is gently deflected, and eventually all the ill will dissipates, leaving the air clear in much the same way as in the last act of "A Midsummer Night's Dream" after the enchantments are broken.

Weldon opens the revels with Richard and Liffey moving from their comfortable London flat to a flower-bedecked, quaintly run-down country cottage. (The change of scene has been entirely Liffey's idea; she is spoiled but charming and always gets her way.) Soon Mabs and Tucker appear, seemingly good-hearted, and generous, but actually more like a female Oberon and her hapless Bottom.

They watch Richard's and Liffey's every move, and Mabs quickly feels hatred mixed with scorn for the soft, inexperienced newcomers. It is not even enough to satisfy her when Richard, loathing the commute and disgusted with the inconveniences of rural life, forsakes Liffey for the familiar comforts of the city during the week. No, nothing will gratify Mabs but that she force Liffey off her high horse, humiliating her and rubbing her face in the awareness that the world doesn't revolve for Liffey alone.

Mabs' arrogance is what betrays her; eager for power over Liffey, she slips the younger woman a potent aphrodisiac and then dispatches a not-exactly-unwilling Tucker over for a visit soon after Richard has exited. The inevitable occurs (the next day, Liffey is not sure if the bizarre coupling wasn't a dream), and Mabs is grimly pleased. But when Liffey then reveals herself to be pregnant, Mabs' hostility erupts into sworn enmity, against both Liffey and the unborn child. It never occurs to Mabs that the baby is not Tucker's; she cherishes her own fecundity and believes in it so implicitly that, when she for the first time is unable to conceive, she convinces herself that Liffey is carrying a child meant for Mabs and deposited in the wrong womb. Summoning up all the expertise her matrilineal heritage offers in the way of gathering "mugwort and comfrey, cowslip and henbane," Mabs begins her campaign to make Liffey lose the baby. Meanwhile, back in London, Richard is feverishly forming unsuitable sexual liaisons -- with his secretary, with an au pair, with a cookbook author who stops pretending to be Liffey's friend as well -- and unsuccessfully trying to dislodge the antisocial sublet tenants of his and Liffey's apartment who are systematically wrecking it through malice and inertia.

Throughout all of these events, one character is simultaneously centerstage and in the wings: the developing fetus itself. Weldon, combining an ironic attitude toward the union of sperm and ovum with matter-of-factly recited clinical detail about the progressive stages of gestation, casts the infant Lee-Fox as the novel's familiar. So, in the 10 brief chapters titled "Inside Liffey," this "lucky, hopeful, still surviving baby" shines out as an elemental spirit counteracting the machinations of Mabs.

From its disarming first pages to its neatly tied-up ending, "Puffball" is a droll and delightful fiction, more "Cold Comfort Farm" than "Rosemary's Baby." With Mabs working her earth-magic and Liffey as the ingenue, it is a contemporary fairy tale about how women, in their differences, are the same.