Private detective Tatyana Ivanova is hired by Alexander Mogilnikov to investigate the death of his college friend Denis Firuzov, who was killed some time ago at a construction site by a concrete block falling from a window. Apart from Denis and the watchman, there was no one else at the site at that moment. And what Denis himself was doing there remains a mystery to everyone. Tatyana is trying to find clues in this strange case, but there is not a single witness to the crime...