The poem retells a famous episode from Ferdowsi's Persian epic Shahnameh relating how the great warrior Rustum unknowingly slew his long-lost son Sohrab in single combat.

Arnold, who was unable to read the original, relied on summaries of the story in John Malcolm's History of Persia and Sainte-Beuve's review of a French prose translation of Ferdowsi.

Sohrab, grown to young manhood and longing to find his father, takes service with the Tartar king, Afrasiab, hoping to draw the attention of Rustum by his feats of arms.

Dying on the sand he declares that Rustum, his father, will avenge his death; and in the affecting scene which follows, the truth at last comes out by means of a seal pricked on Sohrab's arm by his mother.

At the close of the poem the father is left mourning over his son by the banks of the Oxus; and the poet's description of the river's northward course under the stars and moonlight to the Aral Sea affords relief from the emotional tension of the story.