Nobody claims responsibility for the two bodies found in and near a Ford Cortina on Glencraigie Hill--even though John McCarthy, one of the dead men, was a washed-up IRA informer who was an obvious candidate for assassination. Superintendent Cecil Megarry, a hard-bitten cop more interested in the world's problems than his own family's, keeps turning up other mysteries about the deaths. For one thing, McCarthy, an old friend of the father who still rules Megarry's conscience even in death, was shot with a different weapon than was farmhand David Stewart, and a good four hours earlier. For another, Stewart turns out to have a bank account of ú32,000 and a history of accusations for child molesting--which the local inspector has been soft-pedaling for reasons that don't satisfy the relatives of eight-year-old Julie McClenaghan. Finally, McCarthy--though not Stewart--was executed in the same way as a dead milkman with IRA ties. What do the murders have to do with the untraceable ``Bobby Rossi'' in McCarthy's past? Are they political or private? Are they even the work of the same killer? A bare-bones procedural, neatly solved by newcomer Megarry despite the absence of any strong individual footprint; from workaholic cop to IRA faithful, we've all been here before.