Romeo and Juliet: this story is set in Italy, in Verona, where two families, the Capulets and the Montagues are in a fight.
One day, at a mascared ball, Romeo meets Juliet and the two teenagers fall in love. When she goes home, she realises that he's a Montague, so even though she loves him, they can't be a couple. Romeo hears that, and tells Juliet not to worry, because he loves her. The two teenagers go and immediately marry in secret: Friar Lawrence helps them. (Juliet was already promised to Count Paris, an old man).
The day after, Romeo has a fight with Juliet's cousin and becomes an assassin. He's banned from Verona and has to go to Mantua.
Juliet is desperate because now that Romeo is in Mantua, she will have to marry Count Paris. So, asks Friar Lawrence for help: he gives her a portion that will put her to sleep for a few days, as if she was dead. Friar Lawrence will send a letter to inform Romeo, so, when she wakes up, they will be able to run away.
The letter comes too late, and Romeo has already been informed of Juliet's death. So, he runs to Verona, and when he sees Juliet's body, he takes a poison and dies. When Juliet wakes up, Romeo is dead. So, she takes his dagger and kills herself.
After this tragedy, the two families, repented of their useless fights, make peace.