The Enterprise collides with a black hole and is thrown back to Earth in the 20th century, where they must find a way back and erase any trace of their presence. Matters become complicated when they rescue an Air Force pilot and cannot return him without changing history…but if he disappears that will change history as well.
I’m watching Star Trek 1×19 “Tomorrow Is Yesterday” https://trakt.tv/shows/star-trek/seasons/1/episodes/19