In the Bacteriological Institute led by the talented scientist Sergey Alexandrovich Trubnikov, work is underway to create a new medicine to fight terrible diseases. Only the final trials remain. At this time, a “stranger’s shadow” appears in the institute. It takes the form of a certain Professor Okunev—an utterly alien figure in science, a careerist who for his whole life built his well-being on the achievements of other people, posing as their selfless friend: Okunev has become an American spy and has an assignment—to lure from his old friend Professor Trubnikov the secret of how to prepare the new drug created at the institute…