What is Tristan and Isolde about?

In the medieval romance rooted in Celtic mythology, Tristan serves as an emissary for his uncle, King Mark of Cornwall, traveling to Ireland to seek Princess Isolde's hand in marriage. During their voyage back to Cornwall, both Tristan and Isolde accidentally consume a magical love potion that had been intended for the king and his bride. This fateful mistake binds them in an irresistible and tragic love that defies their duty and loyalty to King Mark.