Through a Glass Darkly (S02E06)

Renowned astronomer Marmion gathers the Royal household to his impressive observatory to watch a solar eclipse. The Musketeers and Rochefort escort the Royal household but could never have predicted the twist in fate that ensues. Who is Marmion really and what is his game? The Musketeers are forced into the fight of their lives. Will they accept Milady's help despite their mistrust of her? It might be their only chance to save the King, Queen, and themselves. (BBC America)