The Menaechmi is a comedic play about mistaken identity, a misplaced twin, and the turbulent relationship between an unhappy husband and his unhappier wife.

As the play begins, a professor and clown enter the stage and detail the complex events that led to the play’s confusing circumstances. The two unconventional narrators explain that, many years ago, a merchant named Moschus, embarked on a business trip. Accompanying him on his voyage was Menaechmus, one of his twin sons. Sosicles, the other son, stayed home with his mother. The trip ended in tragedy, as Menaechmus disappears and, unbeknownst to his father, is adopted by a wealthy merchant who lives in Epidamnus. Moschus returns home without his son and promptly dies of heartbreak. 

Sosicles, now the sole remaining twin living in their hometown, Syracuse, renames himself Menaechmus—which was also their grandfather's name—to pay homage to his family’s grief over the missing twin. The twins grow up apart, separated by distance but united by name. Menaechmus of Epidamnus soon forgets his brother, his family, and the circumstances that led to his new life. However, Menaechmus of Syracuse, the former Sosicles, does not forget and, as he grows into adulthood, journeys into the world to search for his long-lost brother. Accompanied by a slave, Messenio, the second Menaechmus voyages to Epidamnus, hopeful for the safe return of his twin. 

Meanwhile, Menaechmus’s life in Epidamnus has fallen to chaos; he quarrels with his wife who, rightfully, believes him to be untrue. Angered by the charges, he calls her a shrew and takes a cloak he gifted her, which he bought for forty pieces of silver, and gives it to Erotium, a prostitute with which he is enamored, in exchange for the promise of dinner with her.

Shortly after, Messenio and the second Menaechmus arrive in the city. Messenio tries to convince his master to give up the search for his lost twin brother, as they are almost out of resources to continue the search. However, the second Menaechmus refuses to stop. Retrieving his brother is important to Menaechmus, and he will continue until he finds his twin. When they leave the ship, Erotium’s servant recognizes him but does not understand that it is a case of mistaken identity. Messenio convinces him that the encounter was because the scammers of the city have helped the servant know his name, and the pair continues.

Next, Erotium accosts the second Menaechmus, believing him to be her lover. He pretends to know her, reminding her of his gift of the cloak and uses her hospitality to conserve their dwindling resources. When he leaves to sell the cloak under the guise of repairing it, Peniculus, one of the Menarchmus's parasites—a person receiving patronage from him—and accused of abandoning him. The man leaves in a rage and tells the first Menaechmus's wife about Erotium.

The first Menaechmus tries to get the cloak back from Erotium to return it to his vindicated wife, but she thinks she already gave it to him and is enraged. The second Menaechmus runs into his twin's wife and does not understand why she is angry at him, why she claims to know him, or why she feels the cloak is hers. Woefully confused, Menaechmus of Syracuse struggles to clarify his circumstances. His brother’s father-in-law soon arrives, conjured by his daughter, and accuses the second Menaechmus of insanity, an excuse the poor twin capitalizes on to make his escape. 

The enraged wife calls a doctor, believing her husband to be mad. The doctors arrive just as the original Menaechmus does and attempt to take him away. Messenio stops...