Henri Castang's cases have increasingly come to resemble Achilles' pursuit of the tortoise: The distance to the goal closes steadily, but never quite to zero. This time, in Freeling's 33rd novel, Castang is in pursuit of Maurice Rogier, a boy kidnapped from his parents four years before. The case has long since been closed, of course, when Anita Rogier insists she's had a phone call from her son. Who could have kept the boy all this time without harming him or demanding any ransom? Perhaps someone with a grudge against Mme. Rogier's father, an SS officer in the war, or perhaps the child he sired on his lover in Prague. So Castang and his protesting Czech wife, Vera, go through the looking glass to what he calls ``Czechland,'' where everything is topsy-turvy--and the languid kidnapper turns out to be a procurer of women to the Danish trade; Vera casually finds the boy while Castang is in Berlin following a quarrel; and it's not unheard of, after all, to find a seacoast in Bohemia. Even more whimsically underplotted than You Who Know (1994), with the mystery rather endearingly mixed with travel notes and aperáus of Castang--by now, surely, the most thoroughly revealed of fictional detectives.