In the two-line Prologue, the speaker warns audience members to “get up and stretch your loins” (1) while they can because “[a] long play by Plautus is coming onstage next” (2). Critics have suggested that these lines were added after Plautus’s death for revival performances.

As Pseudolus, Simo’s slave, and Calidorus, Simo’s son, emerge from Simo’s house, Pseudolus asks a dreary Calidorus what’s troubling him. He wonders what Calidorus has written on his tablet and points out that he’s always been Calidorus’s “closest confidante” (17). Calidorus says Pseudolus “must find my heart in that wax” (33) and that like “the grass of summer” (38), he has been “quickly […] mowed down” (39).

Pseudolus, making fun of the handwriting, reads the tablet and learns that Calidorus’s lover, Phoenicium, has been sold by her pimp, Ballio, to a Macedonian soldier, who left partial payment before leaving. Phoenicium despairs that the man who is supposed to bring the rest of the payment, along with a seal that matches that left by the soldier, is coming today; she begs Calidorus to provide the rest of the payment himself so she can go with him instead.