Grease is a musical movie that was set in the 1950's era about the young love of the good girl, Sandy Olsen (Olivia Newton John) and the bad boy, Danny Zuko (John Travolta). Their budding romance all started in the summertime on the beach. However at the end of the summer, Sandy (aka the good girl) was supposed to be leaving to return to Australia. So, Sandy and Danny were to be parting ways. Unbeknownst to Danny, Sandy ended up not having to return to Australia and this is where the actual movie takes off.
Sandy and Danny both are starting their senior year at Rydell High both thinking of each other, but relay the story to their friends a bit differently. Sandy totally romanticizes their love story and Danny makes it out to be hot and steamy to his friends, so as not to come off as a square or a dweeb to his friends in the very famous musical number, "Summer Loving".
From there, the pair are on a crash course via the snooty and sleazy, (Betty) Rizzo (Danny's jealous ex-girlfriend, played by Stockard Channing) to coming face-to-face again at the high school bonfire. Once they do indeed see each other again, Sandy is ecstatic at first, but her hopes are soon dashed when Danny starts to act all coy and uncaring to please his close watching friends.
By the way, Rizzo has her own on again/off again affair with Danny's best friend, Kenickie (Jeff Conaway), but they are just the supporting roles to Danny and Sandy.
Just when you think these two won't ever get back together, they somehow manage to beat the odds and plan on going to the big high school dance happily together (singing and dancing their way through it). Yet another twist of fate at this dance and they are split apart yet again by friends and nasty high school rumors. And some more singing, a drag race and an end of the school year carnival also takes place.
However, the music and the pair just are very likable indeed to their friends and even their teachers, too. Danny and Sandy are to all that know them by the end just the typical high school sweethearts that somehow can beat all the odds and end up together even through their friends constant meddling. You will just have to watch and find out how.
The end of 1978's Grease might have seemed at first glance like a happy resolution, but a Reddit thread speculates that the movie's final scene has a very grim subtext.