Early on a sunny morning, the postman delivered to the Royal Society, the English Academy of Sciences, a letter from an extremely angry American scientist. “Some Kelvin has begun to lay claim to the galvanometer, which, as the whole world knows, the respected Sir William Thomson invented!” The American was indignant at the audacity of the impostor, the indifference of the Royal Society, and wondered why Professor Thomson himself was silent. William Thomson and Lord Kelvin are two names inextricably linked in the history of science. Why did this happen, what is the contribution to science behind each of these names, and what was the International Astronomical Union guided by when it named the cape on the Moon after Lord Kelvin in honor of William Thomson. The film tells about a grandiose event - the laying of a telegraph cable along the bottom of the Atlantic between the Old and New Worlds. Almost a detective story, as a result of which a new era in the history of mankind was opened. Today's age of communications began precisely then: Great Britain during Queen Victoria, the middle of the 19th century, William Thomson and Lord Kelvin.