Below is a brief summary of the content of the poem's different parts: Prelude The 'Prelude' starts with a hymn to love and then places Iseult among the twelve beautiful women of myth and story, each of whom represents a different month of the year.
Swinburne tells of the lovers' fortunes in Tintagel, which abruptly end when the evil knight Palamides carries Iseult away.
After Tristram has chased and killed Palamides, the lovers retreat together to a bower in the woods and are allowed the first full consummation of their love, which Swinburne describes in abundant detail.
While outside her window the sea and the night-winds battle it out, she delivers a dramatic monologue full of violent blasphemy and bitter lamentation, at the end of which she ruefully watches the sun rise and breaks down in tears.
Joyous Gard To his dismay Ganhardine the brother of Iseult of the White Hands then discovers that his sister, notwithstanding her marriage with Tristram, still remains a virgin.
As it happens, King Mark is out hunting when the men arrive, and Tristram flees with Iseult of Ireland to Camelot, where they finds grace from Launcelot and Guinevere, that other famous adulterous couple.
By their grace Tristram and Iseult are allowed to stay at Launcelot's seaside castle Joyous Gard, where they enjoy their second sustained period together, sweetly conversing about their love.
The Wife's Vigil At the same time over in Brittany, Iseult of the White Hands grows bitter with the shame of her unconsummated marriage; looking out over the British channel she vows, in the poem's third dramatic monologue, that she will take revenge upon her husband by whatever means fate will give her.
He then defeats the evil knights but is wounded fatally in the event, and only with great difficulty does he manage to reach the castle where his wedded wife, Iseult of the White Hands, awaits him.
The Sailing of the Swan The poem's last canto begins with a long hymn to fate, and tells of the final fortunes of Tristram and Iseult.