The characters in this play are two sets of twins who are by appearance identical and were separated at birth without their knowledge. Antipholus of Ephesus and Antipholus of Syracuse are one set of separated twin brothers, born of Egeon and Emilia. Their servants are Dromio of Ephesus and Dromio of Syracuse, twin brothers that each serve their respective Antipholus and are also unaware the other exists.
The play begins when the two Antipholus' twin's elderly father, Egeon, is stopped from entering Ephesus. He has come from Syracuse and risks his life if he is found inside the city walls if he can't pay an expensive fine.
Egeon pours his heart out about his sad life to Solinus, the Duke of Ephesus. He tells Solinus that as a young man he had been married and had twin sons. When a poor woman in town had a set of twins, Egeon bought them to be slaves for his sons.
When crossing the sea by ship, a violent tempest erupted on the ocean separating Egeon and his wife Emilia. Egeon tied himself to the mast of the ship with one of his sons and one of the twin servants. Emilia and the other twin set were rescued by a different boat, but Egeon never saw her or the boys be rescued and never saw her again. Egeon's boy Antipholus of Syracuse set out with his Dromio of Syracuse on a quest to find their long lost brothers but never return to Syracuse, prompting Egeon's search.
Duke Solinus grants Egeon one further day to pay the fine for entering the city. Coincidentally, this is the same day that Egeon's Antipholus arrives. He gives Dromio some money to book an inn but then runs into the other Dromio and believes his own servant is trying to make a fool of him. A series of further confusions take place with everyone's identities that make the Ephesian Antipholus' wife insecure and all parties very confused.
Both Dromio's are beaten for insubordination and the Ephesus' Antipholus and Dromio think they plagued by witchcraft. Antipholus from Ephesus is denied entry back to his home while his brother is inside falling in love with the sister of his brother's wife.
The Antipholus and Dromio of Syracuse are greatly disturbed by all the complications and decide to leave Ephesus. On their way to make travel plans several other instances of mistaken identity occur which end in Antipholus of Ephesus being jailed for refusing to pay a bill. This literal comedy or mistaken identity continues until the Abbess of Ephesus finally introduces both sets of twins.
Citizens of Ephesus are relieved to begin to comprehend the confusion from the two sets of twins and everyone is reunited. The Abbess' identity is revealed as none other than Emilia, Egeon's wife, and Egeon is pardoned.
A Comedy of Errors is one of only two plays Shakespeare wrote that follow Aristotle's classical unities. The classic unities were a frame of reference Aristotle created for stories that required they have three unifying themes. The first unity is action, specifying the play should have only one main source of action as opposed to multiple subplots. The second unity is time, specifying the play's action should be limited to a time span of 24 hours. The third unity is place, and specifies that the action of the play should remain in one physical space and the writer should not try to have the stage represent more than one sole location.