Reader, why did she marry him?

If it hasn't already been done, someone should write a thesis on the influence of pop psychology on the modern novel. I keep being arrested mid-sentence by a sudden impression that what I'm reading is a case history. Novelists are obsessively analytical, but the irony is that this leads down predetermined avenues that have already been so thoroughly explored that things become too simple. Philippa Gregory's readable and insidiously gripping new novel could be summed up as being about a post-natal depression that harks back to unresolved childhood trauma. Fair enough: it's a language we understand, but it does make for predictability.

For this reason, Ruth Cleary, central character of The Little House, is far less interesting than her mother-in-law, the frighteningly charming and helpful Elizabeth who is never fully explained to us. She just does what she does, with fatal consequences.

Orphaned and uprooted as a child, Ruth is now married to handsome TV presenter Patrick. An ambitious and confident radio journalist at the start, she allows herself to be bamboozled by his domineering family into an unwanted pregnancy and the role of "little Ruth" in the little house at the end of their drive - popping pills and weeping, unable to cope with her screaming baby. Step by relentless step, the implacable triumvirate of Patrick, Elizabeth and nice old buffer Frederick patronise Ruth to the point of madness, separating her from friends, career, baby and will, until therapy steps in like a rescuing knight.

Ruth's sanity is frequently affirmed by herself and her analysts. However, I found myself doubting the wits of a woman who could marry a man whose idea of seduction is to call her "Mrs Cleary" while trying to get her into bed. This raises a question that recurs in books about put-upon women. Why on earth did she marry him in the first place? Why on earth is she so wet? Philippa Gregory goes out of her way to give sound psychological reasons for it all, but Patrick's creepiness is made so glaringly obvious that it remains hard to see how Ruth missed it.

The Little House is described as a chiller, but this is misleading. Chilling it is, but only in retrospect. First and foremost it is a domestic drama. Gregory is never better than when chronicling the horrors of supermarket shopping with a vomiting baby, or cranking up murderous resentment over such things as the choice of curtain material. Steadily paced and well sustained, the book builds convincingly to an awful act. It subtly undermines itself at the very end, when, having sold us the metaphor of human beings as fizzy pop ("it's bottling it up that's crazy, letting it out is sane"), it proceeds to the consequences of Ruth's uncorking and leaves us with the impression that, while she is cured in the superficial sense, a silent plunge into yet deeper psychosis is only just beginning.