Why French policemen look so relaxed : MEXICO SET by Len Deighton (Knopf: $16.95; 374 pp.)

The domestic arrangements of spies can be as complicated as the machinations of the KGB. Where will the kids go to school? How can one pay the nanny and the mortgage? Will the old car last a few thousand more kilometers?

These are the kinds of problems bugging Bernard Samson in Len Deighton’s second installment of his trilogy about the spy whose wife defects to the East. Samson must not only deal with the typically opaque difficulties of spying (Has the KGB officer Samson been ordered “to enroll” a plant?), he must also listen to a lecture from his father-in-law, bent on stealing his children, about his impossible finances. Then there’s the brother-in-law who must be convinced that Samson is not sleeping with his wife, the sister of his own traitorous mate. Furthermore, he has to face down a kangaroo court convened to accuse him of double-agentry. And all this happens in between trips to Mexico City, Berlin, obscure parts of the border between the two Germanies and Paris, where a low-grade Soviet agent is poisoned a few minutes after Samson interrogates him. On most of these excursions, Samson is accompanied by the insufferable Dicky Cruyer, a man whose chief concerns are office politics and his own comfort.

Yet Samson does not become a screaming madman. He handles himself with the aplomb and cynicism of a typical Deighton hero--tongue-lashing his superiors, finding decent lodgings where the food is at least passable, bringing off the mission with a minimum of fuss in the face of submachine guns.

Also in typical Deighton fashion, there is low-key wit, written so smoothly that it sometimes takes a second reading to catch the punch line. Here’s one of the less subtle examples:

“There is no habeas corpus in French law. There is no method whereby a man unlawfully detained may be set free. The prefect of police doesn’t need a formal charge or evidence that any crime has been committed, he needs no judicial authority to search houses, issue warrants and confiscate letters in the post. He can order the arrest of anyone. He can interrogate them and then hand them over for trial, release them or send them to a lunatic asylum. No wonder French policemen look so relaxed.”

Nearly all of the characters who appeared in “Berlin Game” are back in “Mexico Set.” The notable exception is Samson’s wife Fiona, who jumped to the Red side in the first volume. True, she issues a personal warning to her husband in a drive around an airport, but Samson never sees her face. Fiona’s plots on behalf of her new colleagues are her contribution in this middle book. No doubt, judgment will be passed on her in the next installment.

“Mexico Set” is good, supercilious fun. Deighton has written an entertainment that’s a mixture of domestic messiness, tangled professional motives and jaded travelogue. It should satisfy the soap opera needs of John le Carre fans and the political addiction of Graham Greene devotees. Not to mention all the readers who want more Deighton. There’s only one complaint. The book cover is an abomination, a garish pink neon, gold, black and white monstrosity obviously designed to shout from the shelves.