Cardinal Richelieu, advisor to Louis XIII of France, instructs musketeers d'Artagnan and Porthos to infiltrate a secret society plotting the assassination of the king. Learning the Duke de Montserant is the leader of the insurgents, d'Artagnan enlists the help of Diana and the two fall in love. The musketeers brand Count Savignac and Montfort as conspirators, marking an "x" on their foreheads.