• Aesculapius Carboy, a chemist in love with Laetitia, tenor
• Eliza Smith, in charge of the refreshment stall, soprano
• Thomas Brown, but really the Duke of Islington, baritone
• Laetitia, soprano
• Mr. Grinder, her father, a retired grocer, bass-baritone

The Zoo contains very attractive music. The chemist’s song foreshadows Nanki-Poo’s entrance in The Mikado. A very amusing quartet is sung by the four lovers: two of them sing in lofty style, while the other couple is discussing the food and drink to be had at a Zoo. First they sing separately, then together! There is a hilarious scene in which the crowd gives well-meant though contradictory advice when a gentleman has fainted. Then there is a chorus that must be sung very softly and politely; and of course Eliza’s song about all her lovers, whom she can no longer tell apart.

A young chemist is in love with a grocer’s daughter, whose father proves uncoöperative. In despair, the young man wants to jump into the bear-pit. There is a certain Thomas Brown, seemingly just an ordinary man but actually a duke in disguise, who is in love with the lady who serves tea at the Zoo pavillion. To prove his love he orders and consumes everything she has in store, which is too much for his stomach and makes him faint. Bystanders restore him to consciousness and in doing so discover his true identity: loosening his coat they find he is wearing the insignia of the Order of the Garter. The story takes a complicated course: the grocer pronounces a curse on his daughter and the despairing chemist; when the tea-serving lady learns that she is to be a duchess she announces that she’d rather stay with the animals. Subsequently the duke buys up the Zoo and offers so much money to the amorous chemist that his beloved’s father waives his objections. In the end the two couples find happiness, the crowd cheers them, so do the animals, and – yes, sir! – Brittania rules the waves.