Banker-sleuth Mark Treasure (Treasure by Degrees, etc.) is off on a cultural packagetour to Leningrad with actress-wife Molly--and they arrive in Russia just as a tiny, priceless Raphael is stolen from the Hermitage. (The theft sequence is dandy.) Could this timing be more than coincidental? Maybe so--because one of the tourists in Treasure's group, a reclusive young musician, is stabbed to death during the intermission of Boris Godunov at the Kirov Opera. At first suspicion falls on a British-Jewish couple in the group, but they're guilty only of smuggling cash to Leningrad refuseniks. So Treasure, in charming tandem with a highly civilized Soviet cop, looks elsewhere within the tour group--which includes a minister, a grande dame or two, a swinging nobleman--for ""a machiavellian operator with a first-rate twisted mind."" Substantial red herrings, a fairly clever windup (including some sleuthing back in England by Treasure's hapless sidekick Peregrine Gore), easygoing comedy--plus neat Leningrad sightseeing: just about the jolliest Treasure package yet, strong on old-fashioned fun but free of the giddy, farcical excesses that have made some previous Treasure outings rather tiresome.