On her journey to Paris the queen of England, Henrietta Maria, also the sister of King Louis is robbed of the crown jewels, which has to be sold in order to finance England's armed forces. The Musketeers quickly discover the thief to be Émile Bonnaire, a flamboyant but pathetic criminal they encountered previously. Athos, Porthos and D'Artagnan pressure Bonnaire into leading them to the diamonds' buyers to recover them. Aramis on the other hand, reconnects with Pauline, a childhood friend he grew up with in a bordel where their mothers lived and worked. She is set to marry a French nobleman but is being blackmailed by someone threatening to reveal the circumstances of her childhood, and Aramis tries to resolve the situation peacefully.

A riot is taking place at the prison, the king has his hands full with his son's birthday.