In her best recent effort by far, Egan handles a well-worn theme--the return to the rich family fold, after a disappearance, of the heir presumptive--with smooth professionalism. Tommy Traxler, kidnapped at age five, turns up 20 years later, claiming to have been abandoned and brought up in a boys' home as ""Jerry Smith,"" Moreover, Jerry/Tommy has enough on-target info about his baby years to convince widowed Ruth Traxler that he is indeed her long-lost son. But Ruth's worried niece Charlene, unconvinced, hires attorney/sleuth Jesse Falkenstein to find proof that Jerry/Tommy is a phony. And Jesse, with help from his brother-in-law (a police detective), seeks out all possible witnesses: the household members at the time of the kidnap; the people at the boys' home; even the FBI, which has some interesting theories about radical-union motives behind the kidnapping. Eventually, however, all the evidence is inconclusive--till the speculation is brought to a screeching halt in a fiat-footed, disappointing finish. Still, despite the washout of a windup: modestly engrossing work from an erratic veteran in trimmer form than usual.