MARY McCARTHY'S LATEST NOVEL is a story about a hijacking. A plane flying to Iran, in the days before the Iranian revolution, is captured by a handful of terrorists. On board are a group of wealthy art collectors, an international committee of liberals planning to investigate rumors of torture in the Shah's prisons, and assorted other passengers. The assorted others are feed almost immediately; the art collectors and the liberals are flown to an isolated farm in Holland, where negotiations for their release drag on and on.

Jeroen, the terrorists' Dutch leader, intends the capture of the liberals, "just men on an errand of mercy to the Third World," as a blow at the "core of the West's pious notion of itself." He also enjoys the idea that he is calling society's bluff -- forcing governments to ransom people whom they publicly praise but privately find troublesome.

The capture of the art collectors, on the other hand, is no more than on afterthought. Jeroen suddenly decides to hold these people too, not for money (which they would never miss) but for their most treasured paintings: a Vermeer, a Titian, a Bosch, among others. The fact that he himself is a frustrated artist lends the issue some depth; he is not your average extortionist. He does have some comprehension of the real value of what he is demanding.

What will become of Jeroen, as he paints himself into an ever tighter corner, is an intriguing enough question to keep us with the story for its own sake. But in Mary McCarth's hands a hijacking is not, of course a mere hijacking, and Cannibals and MISIONARIES is something more than another airport thriller. First, there are the psychological quirks -- surprising but, on second though, believable -- that the hostages show under stress: unexpected examples of cowardice and bravery, comic adherences to the old "normal" rituals, illogical urges to protect the terrorists form defeat. As one hostage observe, a hijacking can expose cracks in one's character like fault lines in the earth's crust.

Second, both the leberals and the art collectors are dissected as social classes with the skill and verve that slew the members of THE GROUP . Particularly vivid is the "stately silliness" of the rich, as when one woman asks a man named Van Vliet whether he is connected to the Van Fleet rose. ("As a practicing lady, she was bent on pursuing connections;. . . everyone had to be related, if only to a rose.") Another woman is "tickled that they had been hijacked; it had 'made' her winter, she announced." And listen to them on the subject of their art collections:

"Nobody traveled with their valuables these days. Years ago, Wintie Thorpe, before ha became a vegetable, used to take his Byzantine ivories with him on the steamer to Europe and set one up in his hotel dressingroom every morning on the shaving stand, so that he could look at it while shaving, start the day right, but there were no old-fashioned steamers any more and no shaving-stand. . . Of the present group, only Charles, apparently, could not learn to move with the times; . . .if you turned out his pockets you would be bound to find a few of his "trinkets,' a rare Babylonian shekel or a sweet little Twelfth Dynasty Horus."

As a modern-day comedy of manners, then, the book succeeds brilliantly, but Mary McCarthy attempts more than that. She raises several serious issues, particularly that of the function of art as object -- that is, as something to be bought, owned, and displayed or concealed by those who have the wherewithal. It's on this level that Cannibals and Missionaries runs into difficulty. It seems, first, to becasting around for an appropriate focus -- beginning with a wholehearted interest in the committee of leberals and their concerns, then veering belatedly and settling (as much by accident, it seem, as Jeroen himself settles) upon the art collectors, after which we hear almost nothing more than Iran.

In addition, the art issue is discussed so earnestly, so undilutedly, that one is reminded of that television term, "talking heads." For pages and pages, people debate in great chunks of dialogue. (And, as in The Group, everything is clouded by the fact that there is no paragraph break between one character's remarks and another's.) There's further discussion in someone's journal -- retroactive discussion, as it were, that comes to light after the story is finished, as if the author were pausing, amid goodbyes in the doorway, to mention one or two dozen extra thoughts that had suddenly occurred to her.

Take it as pure story, therefore, and as a cool, funny study in human behavior and class differences. When a bored terrorist watches kiddie shows on television, when a gentleman drinker's slow topple into unconsciousness is described as "almost a noble sight, like watching a cathedral pine fall" -- then we remember that this is, after all, a very special writer, sharp and witty and intelligent, and possessed of a deadly shooting-eye.