Magical Mystery Tour : HEADLONG: A Novel; By Michael Frayn; Metropolitan Books; 352 pp.; $26

What would we readers do without the infernally brilliant writers of Britain, of which there fortunately seems to be a limitless supply? Certainly one of the very cleverest is Michael Frayn. Thirteen plays, including the fondly remembered “Noises Off.” Journalism. Novels that have made critics thumb through their thesauri to find new synonyms for “smart” and “funny.”

“Headlong,” his ninth novel, will not give their Roget’ses any time back on the bookshelf. It purports to be the recollections of Martin Clay, an academic philosopher careening a little recklessly into art history, of an extraordinary episode in his life. The curtain rises as Clay, his wife, Kate, who is a genuine art historian, and their small baby arrive at their musty country cottage. Their domestic tasks--getting the place aired out and ready--are immediately interrupted by a visit from the bumptious local squire. He seizes on them as neighbors and invites them to his big house for dinner. Clay is annoyed but slightly flattered, a whole literature’s worth of English country squires with grand houses dancing in his brains.

When they arrive, though, they find a place about to collapse, overgrown with tangles and overcome with neglect. The squire’s wife openly hates him and (as angry wives are known to do) flutters her eyelashes at Clay. Meanwhile, it becomes clear why the squire has invited them. Like people exploiting their doctor friends over dinner, the squire means to wheedle some free art consulting. It seems he owns various paintings, now mostly used as screens to keep out the wind blowing down the chimney, that he suspects may be worth something. He hopes to turn them into ready cash and asks Clay to take a look to see what they might be worth. Clay is dubious, modest about his own eye. But the look changes his life. One of the paintings, he is convinced, is a Bruegel (as he spells it), a lost unit of a series depicting the seasons by the celebrated 16th century Dutch painter. Clay immediately sinks into lying and dodging, hoping to keep this news to himself so he can make off with the painting, convinced he would be a better caretaker of a masterpiece than its loutish owner or any potential fat-cat buyer.

The subsequent wheelings and dealings--surprise entrances (nearly, but not quite, “stage left”), slammed doors, inopportune arrivals, farcical misunderstandings, wild departures, “in” remarks to which the reader is made privy--owe everything to Frayn the master comic playwright. Kate’s ladylike jealousy over what she takes, mostly mistakenly, as an affair between her husband and the desperate wife of the squire would do nicely on the stage. Frayn is terrific at moving his characters around, at giving them sharp or funny or dramatic things to say or not say. He also knows his genre novels. The country setting, the tumbledown cottage smelling of disuse, the manor smelling of the end of an era, the noisily self-assertive landowner, the aggressively available wife; all are spoofs several times removed, British jokes about jokes about “types.”

But it’s the large central section of this novel into which Frayn seems to have poured his heart, and here the humor is much less antic. You can’t help feeling as you read this part of “Headlong” that he may have conceived the book backward, with the plot patched on as justification and frame for Frayn’s serious thinking about the malleability of meaning in the arts.

Clay is obsessed with his mystery painting, so much so that he is willing to trample his marriage and his child to get to it. To him it is not merely paint on a canvas--arrangements of color, form, pigment thickness, lightness and darkness, circles and lines--but code. He sifts through the scholarship, trying on one theory after another, struggling to make the painting fit the theory and the theory fit the painting. If they match, then he has a Bruegel. If they don’t--well, then he has a problem.

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Depending on what he reads, the painting is clearly an allegory of Bruegel’s political radicalism. Or, no, it’s a cautious Flemish attack on the barbarities of occupying Spain. Or, yet again, it’s painted religious heresy. Or a message shown by a figure in the foreground that may or may not be there. As he wavers, Clay seems to be painting the canvas himself with layers of significance peeled from conflicting scholarly opinion. Under its influence he sees in it what he wishes to see, at least until each new bubble bursts.

Picking through all this can require Clay’s patience and single-mindedness. Though not exactly rollicking, Frayn isn’t stingy, even here, with the laughs, gleefully pricking holes in the overconfidence of academic art criticism. But just below the sugar powder you bite into his tough-minded essay on how history and individual human folly combine and conspire to manufacture art’s “message.”