Mary realizes she cannot follow her heart and must marry for the good of her country; when Catherine is faced with an accusation, Mary suspects that she is being framed.
Mary relies on Gideon to uncover the truth about Prince Don Carlos; Elizabeth makes a stunning discovery; Narcisse forces Claude to get married to someone of his choosing.
When Mary discovers a dark secret of the visiting Prince of Spain, she asks Catherine for advice in handling it; the new ambassador from English court raises suspicions; Bash's pursuit of the killer comes to a head.
When Oliver learns his mother and sister stopped celebrating Christmas after his disappearance, he decides to throw a Christmas party; Tommy asks Laurel to spend Christmas with him.
An emergency disciplinary hearing at Quantico results in deep secrets being revealed; Alex and her team try to find the real bomber.