In the poem, the woman initially declines her former lover's invitation to fulfill a previous marriage vow. She tells him that she is now married and has two children; therefore, she can't go with him.
The woman's former lover is devastated and maintains that he only returned for the hope of claiming her. Upon hearing this, the woman poses a hypothetical question: if she decides to leave her husband and children, what will her former lover give her? Can he give her anything more valuable than her husband and children?
Her former lover surprises her by saying that he currently has seven ships on the sea; additionally, he was brought to land on the eighth. Upon hearing this, the woman immediately says goodbye to her two children.
Her decision made, the woman steps foot on her former lover's ship and delights in the fact that the sails are made of taffeta and the masts, of beaten gold. Before long, however, her former lover's facial expression changes ("dismal grew his countenance"). Soon, the woman spies her lover's "cloven foot." Here, the cloven foot is a reference to the Devil; the implication is that the woman has been lured to her damnation by him.
The devilish identity of the former lover is confirmed when he tells the woman:
"Oh, yon are the hills of heaven," he said, "Where you will never win."
Oh, yon is the mountain of hell," he cried, "Where you and I will go."
The last stanza reiterates the theme that a woman's consuming desire for wealth will ultimately end in misery.
He struck the top-mast with his hand,/The fore-mast with his knee;/And he broke that gallant ship in twain,/And sank her in the sea.