This play derives its name from the two pairs of brothers who are introduced. Demea and Micio, the elders, had always been very dissimilar in character and manner of life. Micio was a pleasant old bachelor, and had always lived in town, and was very lenient and indulgent towards his young relations. Demea on the contrary had kept up the thrifty habits of his early years, residing on his farm and taking a severe view of the conduct of his sons. Ctesipho, the younger of his sons, lived with his father at this farm; but Aeschinus, the elder, had been adopted by his uncle. They had accordingly been very differently brought up. Ctesipho had been kept very strictly at home, and was, to the best of his father's belief, a model of propriety. Aeschinus had been indulged by his uncle in every way, till he was notorious for his dissipation. He went so far at last as to offer violence to a young lady named Pamphila, whom he met one night when he was intoxicated. This was the last of his excesses. He promised to make all amends in his power by marrying Pamphila, and on this condition the matter was kept quiet by Sostrata her mother. Ctesipho in one of his visits to the town had fallen in love with a music girl belonging to a slave-merchant, and was carrying on an intercourse with her under the cover of his brother's name; for Aeschinus had taken the credit of the affair to himself that his father might not hear of Ctesipho's doings. After a time the slave-merchant gave notice to Ctesipho that unless he bought the music girl at his price she should be immediately sold. Ctesipho was in the greatest despair at this announcement, and was half inclined to run away from his troubles and leave the country, when Aeschinus, hearing the state of the case, cut matters short by breaking into the house of Sannio the slave-merchant, maltreating him, and carrying off the girl to his own house, where she was received by Ctesipho.

Here the action of the play commences. Demea coming into town hears of this new outrage of Aeschinus', and accuses his brother Micio of being the cause of all this excess. It was his indulgence that had made Aeschinus so dissolute. How different was the conduct of his brother Ctesipho who had been brought up strictly at home in the country! Micio in return justifies his mode of education. Meanwhile Aeschinus is busied, with the assistance of his slave Parmeno, in arranging matters with Sannio, who blusters loudly at first, but finds at last that the best plan is to pocket his affront and trust to the young men to pay him, for he will lose more by waiting to prosecute the affair, as he is on the eve of a voyage to Cyprus, than if he abandons the slave altogether. The news of Aeschinus' prank had spread over the city, and it was now carried to Sostrata his destined mother-in-law by Geta her slave, who had witnessed the whole affair. Sostrata sends her trusty Geta to Hegio, an old friend of her late husband Simulus, who will stand by her, and see that her daughter has justice done her. Demea in the mean time is in consternation, for he has heard that Ctesipho was with Aeschinus when this music girl was carried off; but Syrus, one of Micio's slaves, contrives, with great skill, to make the fact increase his good opinion of his son; for he represents Ctesipho to have taken part in the affair only to blame his brother's dissolute conduct, and says that as soon as the matter was over he had returned to the country to his usual work. Demea is greatly affected to find that he has one son who is a credit to his family, and sets off for his farm. On his way he meets Hegio, from whom he learns the circumstances of Aeschinus' connexion with Pamphila; and at the same time he finds from one of his farm servants that Ctesipho has never been to the farm at all, as Syrus had pretended. These news send him back to Micio in a rage; but he is again met with a new fiction by Syrus, who revenges himself on him by sending him on a fool's errand over the whole town to look for his brother. Micio meanwhile has been with Hegio to Sostrata and Pamphila, and has comforted them by giving his consent to the marriage of the young lady and Aeschinus. Demea now returns from his fruitless search after his brother, and there is a general disturbance, particularly when one of the slaves accidentally betrays the fact of Ctesipho's being in Micio's house, where his father finds him with the music girl. After some more discussions between Demea and Micio, the former suddenly determines to change his demeanour; and to the surprise of every one whom he meets, and not a little to his own, he acts the courteous and complaisant man. He falls in with all their humours, and promotes the happiness of all parties. Pamphila is married to Aeschinus; Sannio is paid; Micio is made to marry Sostrata; Hegio is provided for; and Syrus and his wife are freed in consideration of the great services which the cunning slave had rendered to morality. The play concludes with a speech in which Demea explains the meaning of his late conduct, and gives his hearers a little wholesome advice for the future.

ADELPHI. ACTA LUDIS FUNEBRIBUS AEMILII PAULLI QUOS FECERE Q. FABIUS MAXIMUS, P. CORNELIUS AFRICANUS. EGERE L. ATTILIUS PRAENESTINUS, MINUTIUS PROTHIMUS. MODOS FECIT FLACCUS CLAUDII, TIBIIS SARRANIS. FACTA GRAECA MENANDRU L. ANICIO M. CORNELIO COSS.