A Mad, Mad, Mad Adventure in Russia

In Italy, a dying woman tells her granddaughter that she hid her treasure many years ago in Russia, in the city of Leningrad. Other people (who were around when she died) also learn about it. Thus several people arrive in Leningrad trying to find the treasure, each one for himself/herself. What's worse - the only information they have is that the treasure is under a lion - and it's in Leningrad, a city known by its numerous statues of lions. The story gets even more interesting when the soviet militia (police) learns about the whole thing and send an undercover agent...