The Day Before Tomorrow
Original title: Le temps n'a pas d'odeur. Translated into English in 1972.
The Federation considered itself a technological Utopia – and the innumerable planets under its sway were guaranteed stability by virtue of the time-change teams. For whenever a planetary historian located evidence in the past of any newly found world that it might evolve into a possible menace, a team of seven would be sent to tamper with that world's history. But the seven men that went to Ygone encountered a fate no theorist had projected. They met with immediate ambush, they met with a strangely peaceful culture that could not be fathomed, and they finally were confronted with all the contradictions and temporal knots that the whole system of time-change had to imply.
Gérard Klein
Gérard Klein (born in 1937) is a French science fiction author. He is also known as Gilles d'Argyre.