Russian "research ships" keep on appearing unexpectedly in offshore windfarms, in submarine exercise areas and above gas pipelines... and off the German coast, in the Baltic Sea. What is the vessels' secret mission? Why do they often travel with their location transmitters turned off and armed special forces on board? And why is it so difficult for police and military to do anything about these mysterious ships? An international journalist team takes a closer look at Russia's suspected spy fleet and sets out to decode their morse code messages.