Diamonds of Bird Island

Once, Ivan came across an old letter. It doesn't matter that it is written in German, as Ivan is preparing to enter MGIMO and become a diplomat; he diligently studies languages, and his German is at a good level. The... letter is easy to translate, but it's very strange — an unknown officer of the Third Reich writes to his beloved Marta, stating that here, in the north, during his service at a secret fascist base, he has obtained real diamonds, and thus, after the war, a rich and comfortable life is ensured for his family. But there are no diamonds in this region and there never have been! And the war ended several decades ago. Is it possible that a treasure actually exists? The only way to find out is to embark on a quest with the best friends.