King Louis ventures into Paris with the musketeers in disguise as a common citizen. He and D'Artganan get separated from the others in a bar fight. In the alleyway outside, they are both kidnapped and dragged away.

In an effort to remain close to his son, Aramis starts up an affair with the baby's governess. 

The Musketeers begin a frantic search for Louis and inform the Queen that he may miss the Dauphin's christening the next day. Rochefort comes up with the brilliant idea to spread the rumor that the King is sick to explain his absence as foreign dignitaries arrive. 

Rocherfort and Constance butt heads over their differing advice for the Queen. 

On the outskirts of the city, D'Artagnan and Louis are captives of Spanish slave traders. They meet another prisoner named Pepin and rescue him from being beaten by their attackers.

Milday de Winter is in league with the slave traders, and she recognizes the royal seal on one of the rings they took off of Louis. 

Rochefort and the Spanish ambassador Perales discuss how best to use this development to Spain's advantage. Perales wants to have the king assassinated, but Rochefort warns against it, noting that if a coup puts Queen Anne out of power, then they will lose their influence. Perales order the assassination anyway.

Rochefort asks Constance to spy on Anne for him, and she firmly declines.

The Musketeers get a lead on the slave traders whereabouts, and they race out to investigate. Perales hit squad attacks the slavers' camp and Louis, D'Artagnan, and Pepin fight to escape. Pepin dies in the process. Milady de Winter helps them escape, endearing herself to the king with a false tale of her innocence in the slaving business.  

The Musketeers rescue the King, returning him to the palace in time for the Dauphin's christening, but he still blames them for the entire debacle anyway. They then journey to Pepin's house, giving his wife and daughter all the spare money they have as recompense for his death. They tell him Pepin died defending the King, and the money is a token of his gratitude.