Egeus insists that Hermia should marry Demetrius but, she wants to marry Lysander.
Egeus: Hermia! You must marry Demetrius, not Lysander.
Hermia: No! I want to marry Lysander!
Hermia and Lysander decides to run away into the woods surrounding Athens where they can bypass the law and get married. They tell Helena about the plan.
We're going to the forest!
Oberon sends Puck to retrieve a love-juice to put on Demetrius while he is sleeping for jokes. But, Puck comes across Lysander instead and accidentally uses it on him.
Helena finds Lysander and wakes him up, causing him to instantly love her. Oberon sees this, and he realizes that he has made a mistake. So, he puts the love-juice on Demetrius's eyes, who upon waking up, also falls in love with Helena. She thinks that the two men are trying to torment her. Hermia comes across this situation and thinks the two are joking.
Lysander and Demetrius prepare to fight for Helena. Soon after, Puck interferes and leads them through the woods until all 4 fall asleep.
No she's MINE!
They explain why they are in the woods, at a point where Egeus demands that he be allowed to execute the law on Hermia. But, Demetrius interferes and tells them he no longer likes Hermia, but Helena. Theseus decides to overbear Egeus and let them get married.