There are four main plots in Shakespeare's A Midsummer Night's Dream. They're all carefully woven together and there are many characters involved. The first plot involves four young lovers trying to work out their love for each other. The second plot is about a wedding between the Duke of Athens and the Queen of the Amazons. Interspersed with these two plots is another involving some local town peasants who are rehearsing a play for the Duke's wedding, but get interrupted when one of the actors gets transformed and a fairy queen falls in love with him, which is part of the final plot. All these plots make for a very jumbled night.
This first plot is very complicated in itself. Egeus, a friend of the duke's, has a daughter Hermia who is to be married to a young man named Demetrius. Demetrius loves her dearly, but Hermia is in love with another man, Lysander. Hermia's best friend, Helena, likes Demetrius but Demetrius despises Helena. Hermia must marry Demetrius or she will have to become a nun or be put to death, yet she still refuses to be his wife. So one night, she and Lysander run of into the woods together so they can get married later on. Helena sees this and wants to get brownie pionts with Demetrius, so she goes and tells him what has happened and he runs off into the woods to find them, with Helena trailing behind.
While Helena and Demetrius are making their way through the forest, Hermia and Lysander decide to rest on the ground for awhile. When along comes Puck, a mischievous fairy who likes causing trouble. Puck puts potion from a love flower into Lysander's eye, thinking Lysander is Demetrius who he was supposed to do this to, and when Lysander awakes, his love goes from Hermia to Helena. This really upsets both Hermia and Helena for Helena thinks he's making fun of her. Later, in attempt to fix his mistake, Puck puts the potion in Demetrius' eye and he too wakes up to love...