An apothecary in Italy in the year 1560 has two problems: How to sell poison without being caught, and how to stay alive while causing others to die. A powerful Court Official, Da Brescia, arrives demanding poison. A rival covets both his job and his young mistress. The frightened apothecary fears death whether he says yes or no and swears he is not guilty of dealing in poison. Da Brecia insists he will watch unseen and let the apothecary prove his innocence—if he can. The mistress appears and demands poison—for Da Brescia's wife. The next caller is the wife—who seeks poison for Da Brescia. Under threat of death, the apothecary yields to all of them. Then a curious discovery is made. The would-be murderers didn't get poison, but they do get, and the audience with them, a humorous climax, a guaranteed antidote for—shall we say, poison?