Egeon is the father of twin boys, both called Antipholus. Both boys have a servant - both called Dromio. Egeon is separated from his family, and the twins from each other in a shipwreck.
Egeon arrives in Ephesus looking for his family. Antipholus and Dromio arrive in Ephesus from Syracuse in search of their long-lost twin brothers, Antipholus and Dromio. Antipholus, married to Adriana, and Dromio, servant, live in Ephesus. Antipholus and Dromio are surprised to find that everybody recognises them. Antipholus and Dromio aren't.
Suddenly the strangers find themselves greeted like old friends, Antipholus finds that he has acquired a wife, and everyone in Ephesus seems to be behaving very strangely...