A stupid story happened to private detective Tatyana Ivanova: ex-boyfriend Kolya came and demanded his jar of jam back. Having complained about how the men crushed it, Tatyana returned the jar, and then sat down to drink tea with her friend Lena and discovered twelve diamonds at the bottom of a similar jar. So this is what Kolya was looking for! And, it seems, he’s not the only one: unknown people have kidnapped Kolya and Lena and are now blackmailing Tatyana. She would be glad to get rid of the stones, but they mysteriously disappeared from the hiding place in Lenin’s apartment. And then the real owner of the diamonds showed up, who was told by the police that only Ivanova, the best private detective in the city, could help him. So Tatyana faces a difficult task: to save her friends and find the precious stones...