The years preceding World War II are often called the period of intelligence struggle. So Professor Burago’s discovery could not leave hunters of other people’s secrets indifferent. Of course, the scientist’s research made it possible to hide ships, submarines, and airplanes from prying eyes! Alexander Naydenov and Pavel Zhitkov have to engage in a merciless struggle with the Nazis, who are not going to stop at nothing... The famous novel by the author of many Soviet bestsellers, which the whole country was reading half a century ago.