This blue rose will tell you what my heart has known for a long time... Slovak production of the famous operetta by Gejza Dusík and Pavel Braxatoris. Marseille. Engineer Lenoir futilely fends off journalists interested in his latest invention. It is not yet finished, but already foreign countries are interested in it, and even foreign secret services are getting their teeth into it. But Lenoir needs to finish his "death pill" in peace. So he hires the police to protect him. He plans to finish the job on the cruise yacht of a Kanuche factory worker, which the police prefect himself recommends as the perfect disguise. But the true purpose of the engineer's "trip" is overheard by a sensationalist reporter, Philippe Plafeau, who sneaks onto the boat disguised as a lifeguard. But he's not the only one. The other lifeguards are actually undercover police officers. Lenoir's new butler is also not who he says he is, nor is the suitor of Lenoir's daughter, Count Dubois...