Ariel (Halle Bailey) is the youngest daughter of King Triton (Javier Bardem), the ruler of the underwater kingdom Atlantica. Fascinated by the world of humans, Ariel falls deeply in love with the handsome Prince Eric (Jonah Hauer-King) after saving him during a shipwreck and resolves to meet him in the world above water.

Her quest brings her in conflict with her father and in the clutches of the scheming sea witch Ursula (Melissa McCarthy).