Egeus, Hermia's father wants her to marry Demetrius, but she is in love with Lysander. Theseus rules that in four days, Hermia will have to decide if she wants to marry Demetrius, become a nun, or be put to death.
Hermia and Lysander decide to run away to the woods, to be free and get married, outside of Athenian rule. Before they go, Hermia tells the plan to her best friend Helena. Helena (who is in love with Demetrius) tells Demetrius and they follow the into the forest.
We will all have a triple wedding.
Oberon, the fairy king, sends his servant, Puck, to put a potion in an Athenian's eyes (meaning Demetrius) so that he will fall in love with the woman who loves him (Helena). But, Puck finds Lysander first, who is then awoken by Helena and falls in love with her.
After Lysander and Demetrius fight over Helena and Hermia gets mad, Puck puts an antidote in Lysander's eyes, but not Demetrius. Then, the 4 lovers wake up, and Demetrius loves Helena while Lysander loves Hermia once again.
The lovers are met by Egeus and Theseus. This is the day when Hermia has to decide what she will do. Demetrius steps up and tells Egeus that he no longer loves Hermia. This causes Theseus to give the new option of a triple wedding, which pleases all the lovers.
All three couples are married and everyone is happy. The play takes place and everyone likes it. Everyone then lives happy lives forever.