England, 1930s. The world is being torn apart by two opposing ideologies; Communism and Fascism. For many across the globe, it is a fight between good and evil. Four young men meet in Cambridge and conspire to change the world for the good. Kim PHILBY is an idealistic undergraduate desperate to act against the evil of Fascism which is already thriving in Germany and Italy. He's sick of talk. He wants action. He wants to be at the heart of the only force he believes powerful and charismatic and idealistic enough to conquer the horror now poised to spread through the rest of Europe. He wants to join the Communist Party. As Party recruiters, Guy BURGESS (a fellow undergraduate) and Anthony BLUNT (a young Cambridge don) can get him in. But first, they want Philby to persuade his close and well-connected friend, Donald MACLEAN (also undergraduate), to join with him. Maclean, the son of a Cabinet minister, is an attractive prospect to the Party; Philby - middle-class, non-elite, over-keen - is less so. Philby and Maclean are tested, and pass. But while Philby is overjoyed at their success, Maclean is ambivalent and sad: he feels by joining the Party he would be betraying everything his father has stood for. Philby is resolute: Communism is the only moral choice in this polarized world. Then Maclean's father dies, and Philby is forced to exploit Maclean's grief and vulnerability to convince him to join his friends and fight the good fight. Maclean does join, and Philby's place in the Party is secured. Finally, Philby's righteous struggle can begin. The Party sends him to Vienna: another test, though Philby imagines he's making a vital contribution to the 'cause' against Fascism. There, he meets a fiery young Jewish Communist, LITZI, who daily risks her life and the security of her family to wage guerrilla warfare against the oppressive, pro-Fascist government. Philby is inspired by her actions, her commitment, her huge risk-taking. He falls in love, and starts to help her. After a catastrophic mission, Litizi's life is in danger: Philby's overwhelming love for her is clear when he proposes they marry and flee Vienna together, as husband and wife. The newly-married couple arrive in England and re-join old friends; Maclean, Burgess, Blunt. Blunt - guided by the concerns of their Soviet contact, Otto - is wary of Philby's marriage to Litzi. She is a known Communist. She is an activist. Her politics are transparent, there for all to see. This is not the life Blunt and Otto imagined for their star recruit. Litzi, they tell Philby, has got to go. And if she doesn't?, Philby asks. Then there will be no place for Philby in the Party. A crucial moment for Philby - a decision which will shape the rest of his life. Love or Politics. Marriage or the Party. Life or the Cause. He chooses the Cause.