The king's cousin is ambushed while under Musketeer escort as she travels from Mantua to Sweden to make a political marriage that will be advantageous to France. The Musketeers must quickly discover who is targeting her to keep both her and the alliance between countries protected.

However, it emerges that other important figures at court also appear to be in danger. Who is the killer and could he already be inside the palace walls?

The Musketeers must put their lives on the line when the queen is accused of treason. They have no choice but to steal her away from the palace to safety while they search for evidence to prove that Rochefort is a Spanish spy. However, it soon transpires that nobody is safe from Rochefort's grasp, not even the king.