Cardinal Richelieu has, after his other underling's repeated failures, asked Milady to make sure Juliette can't organise the meeting between the Duke of Buckingham and Queen Anne. Juliette is still on the run from the Cardinal's guards and manages to run into Planchet and Sandy, using Sandy to escape. Milady is in a nearby coach when Planchet and Dogtanian are discussing what's happened, from there she lures Dogtanian into her house.
When Dogtanian is in Milady's house she offers him a drink, really a hypnotic drug and in his suggestible state tells him to kill the Queen. Dogtanian makes his way to the palace and easily beats the unsuspecting guards on his way in, Dogtanian enters the Queen's bedroom as Juliette is telling her the Duke of Buckingham's plan. The Queen and Juliette manage to stop the assassination covering Dogtanian and hitting him with a chair, six times. This does manage to knock Dogtanian out of his trance without any permanent physical or mental damage and Juliette leads him through a secret tunnel before Richelieu and King Louis enter.
On their way down the tunnel Juliette slaps Dogtanian (because a brutal chair attack isn't always enough) for being seduced by Milady and reveals that she loves him. Dogtanian ends the day jumping for joy when the Three Musketeers and Treville ride along.