Act IV opens with a “dumb show”—a theatrical moment of mimed storytelling to further the plot. Alonzo is missing. Beatrice marries Alsemero with Vermandero’s blessing. De Flores watches, smiling, until Alonzo’s ghost appears before him. They all exit. The dumb show is complete.

After the wedding, Beatrice frets about her wedding night. She’s no longer a virgin, having slept with De Flores. She worries Alsemero will discover this, bringing her shame and dishonor. Beatrice finds Alsemero’s private closet and looks inside, finding vials and a manuscript of science experiments titled Secrets in Nature. The vials contain potions that, when consumed, reveal if a woman is pregnant or a virgin. The latter potion makes a virgin “incontinently gape, then fall / into a sudden sneezing, last into a violent laughing; / else dull, heavy, and lumpish” (4.1.48-50).

Diaphanta enters. Beatrice forms a plan for the virgin Diaphanta to slip into Beatrice’s bedroom that evening and switch places with Beatrice without Alsemero knowing. That way, Alsemero will think Beatrice is still a virgin when they consummate the marriage. Beatrice confirms Diaphanta is a virgin by giving her Alsemero’s potion. Diaphanta exhibits the noted effects. Beatrice also takes the potion, which has no impact on her.