The story centers around a practical joke played on the queen by Don Sallusto for revenge. Knowing that one of his slaves, Ruy Blas, has secretly fallen in love with the queen, the Don disguises Blas as a nobleman and takes him to court. Intelligent and generous, Blas becomes popular, is appointed prime minister, and begins useful reforms, and conquers the queen's heart. Don Sallusto returns to take his revenge; he discloses the masquerade by cruelly humiliating Blas - he commands Blas to close the window and pick up his handkerchief, while trying to explain the condition of Spanish politics. Blas kills him and decides to commit suicide with poison. On the point of death, he is forgiven by the queen who openly declares her love for him.

Source : Wikipedia