When dense smog cripples London for days and creates a serious health hazard, Churchill’s inaction leaves him vulnerable to his political enemies.

Margaret and Peter come to Elizabeth with a request. With a royal scandal about to break in the newspapers, the Queen Mother intervenes.

Elizabeth and Philip go on an exhausting world journey. Margaret takes over some of her sister’s official duties and tries to liven things up.

Margaret and Peter are reunited, but another obstacle stands in their way. Elizabeth is torn between her duty as Queen and her love for her sister.