June 1888. Student Klim Ardashev is sent to England on a two-week scientific assignment. Even on the ship, he meets an English scientist. They agree to meet in London, but Klim finds him mortally wounded in a tunnel under the Thames. The dying professor asks the Russian student to find his killer. Carrying out the last wish of the deceased, Ardashev becomes involved in a dangerous investigation and even ends up in jail—yet in the end he stays ahead of Scotland Yard in catching the criminal.