A well-known violinist Dorothy Lambert arrives in Bulgaria. Her manager Ted Smiles accompanies her. The Bulgarian intelligence service has received a cipher communication that an agent codename Dolly will try to contact the foreign spying agency's station chief in Bulgaria. The violinist is a Bulgarian who has left for abroad with her parents before WWII. In his native town on the Black Sea, she meets her childhood friend Tinko, now a State Security colonel, sent there to investigate the spy affair. The suspicion falls on the violinist. Ted Smiles hangs around a puppeteer, later on exposed as the chief of station and arrested by State Security men. The police tell Ted Smiles that he would have to leave alone as Dorothy has been detained. He insists on taking along her violin. The violin is checked out and the microfilm found in it identifies Ted Smiles as the spy. He is arrested. Dorothy is free to leave the country but she stays in her homeland.