In this poem, W.B. Yeats narrates the story of Leda when she was raped by the god Zeus in the form of a swan. The first stanza opens with Zeus, in swan form, attacking and subduing Leda so he can mate with her. The second stanza focuses on the actual act of their mating and the violence of it, and the third and final stanza focuses on the act of Leda getting pregnant.
Yeats suggests that through mating with a god, Leda is able to have a vision of the future and sees the horrible fate that will befall Clytemnestra, the daughter she has just conceived with Zeus before he "indifferently" lets her go.