Act I

The action takes place in 200 BC, on a street in Rome, in front of the houses of Erronius, Senex and Lycus. Erronius is an old man whose children were stolen in infancy by pirates. Senex is a hen-pecked husband to Domina, owner of the slave Hysterium, and father to Hero. Lycus is a procurer who has recently received a new shipment of courtesans (Comedy Tonight).

Senex and Domina leave to visit Domina's mother. Hero has caught sight of one of the courtesans, Philia, and falls instantly in love with her (Love I Hear). Pseudolus, Hero's slave, is trying to win money to buy his freedom but gets into trouble. Hero and Pseudolus strike a bargain for both of them to get what they want - Hero his Philia and Pseudolus his freedom (Free). On Hero's behalf, Pseudolus pretends he wants to purchase a lifetime companion. Lycus parades his latest courtesans so that Pseudolus can choose one (the House of Marcus Lycus). Philia is not among them but Pseudolus sees her at a window. Lycus says Philia is a virgin who has been sold to the Captain, Miles Gloriosus, who will be coming to claim her later that day (Lovely). Pseudolus convinces Lycus that the girl is suffering from the plague and offers to house her for fear of contaminating the others. Pseudolus tries to arrrange for Hero and Philia to escape on a boat (Pretty Little Picture) but she refuses, as she must honor her contract to Miles. Pseudolus puts Philia into Senex's house and tells her that Miles will knock 3 times to claim her. He then steals Hysterium's book of potions to concoct a sleeping potion, but lacks an essential ingredient, which he goes to try to find!

Senex returns unexpectedly and kicks the door to his house 3 times. Philia, thinking Senex is Miles, throws herself into his arms, offering him her body but not her heart - which already belongs to Hero. Pseudolus returns and tells Senex that Philia is a new maid (Everybody Ought to have a Maid). Senex arranges to meet 'the maid' in Erronius's house out of the sight of his wife. Domina had left Hysterium in charge, although now everything seems to be getting out of control (I'm Calm).

Meanwhile, Erronius returns home after 20 years of searching for his stolen children. Pseudolus pretends to be a soothsayer. Erronius gives him a ring engraved with a gaggle of geese and mentions that his stolen children have similar rings. To get Erronius out of the way, Pseudolus tells him he must walk around the seven hills of Rome seven times, and then his children will return. Meanwhile, both Senex and Hero are trying to win the affections of Philia (Impossible).

Soldiers announce the imminent arrival of Miles Gloriosus, sending Lycus into a panic, as Philia is no longer in his house. Pseudolus suggests telling the Captain that Senex's house is his. Lycus agrees to bring the courtesans over to Senex's house, and asks that Pseudolus impersonate him (Bring me my Bride)

Act II

Pseudolus tells Miles that Philia has escaped, and Miles threatens to burn down the house and kill Pseudolus (who he believes is Lycus). Pseudolus promises to search for Philia. Domina returns home unexpectedly, haunted by a premonition that Senex is up to no good (That Dirty Old Man). She discovers Miles in her house; he thinks she is a courtesan. She leaves him to find out what Senex is up to and goes in search of a disguise. Hero discovers Philia setting off to meet Senex (That'll Show Him). Pseudolus concocts a plan to disguise Hysterium as the body of Philia who has supposedly died of the plague. (Lovely reprise).

Pseudolus informs Miles that his bride is dead (Funeral). He convinces Miles not to burn the corpse and also manages to get back the contract Miles had with Lycus for Philia. While attempting a goodbye kiss, Miles discovers that the 'corpse' is alive and, panic stricken, Hysterium makes a hasty exit! Miles' soldiers give chase and the courtesans escape too.

Hysterium returns, still dressed as the dead Philia. Senex, mistaking Hysterium for Phylia, sends him to Erronius's house. Domina arrives disguised as a virgin and Senex nabs her, thinking she is Philia and regains his love for her. Erronius passes by on his fourth time around the seven hills of Rome and, seeing a ring that Hysterium is wearing, thinks he is his lost daughter.

Miles seizes Pseudolus and is about to kill him when Pseudolus drinks the 'poison' he believes is a sleeping potion, but which turns out to be an aphrodisiac. Lycus emerges and presents the real Philia to Miles who, in the excitement of finally getting his bride, forgives Pseudolus. However, it is discovered that both Miles and Philia have a ring engraved with a gaggle of geese. This means that they are brother and sister and Erronius is their long-lost father. Hero is now free to marry Philia (Comedy Tonight - finale).