Russia 1903. Von Plehve, the head of security, meets with Tsar Nicholas. He briefs the Tsar on the latest attempts to destroy the revolutionary movements that threaten him. They examine photographs of the most high-profile Marxists (Plekhanov, Martov and Lenin) who are all under surveillance in Europe.

London. Lenin and his wife Krupskaya live in spartan lodgings. Lenin leaves to meet with Martov, and they discuss the coming Social Democratic Congress, and how their group (the board of the party paper Iskra) can become the leading tendency in the party.

The board meets to discuss Lenin's plan to develop the party along more centralised lines. Zasulich, an older member of the board, is worried that the revolutionary potential of the peasants is not addressed, but Lenin has no patience with this. Lenin's view becomes policy.

Lenin and Krupskaya are in bed when they are disturbed by a visitor. It is Trotsky, who is more familiarly known by his Iskra name of 'The Pen'. They talk, and Lenin emphasises to Trotsky that the current enemy is not the Russian state, but anyone who impedes the course of the revolution.

At the next Iskra meeting (attended by Trotsky), the board is split between the programme outlined by Lenin, and Plekhanov's alternative. Martov offers a compromise. This is agreed, but as Lenin attempts to leave, Martov introduces another item of business. Bauman, a party agent, has been accused of impregnating a party member, then slandering her via the party's communications network. The woman has killed herself and addressed her suicide note to the party, causing her husband Miliutin to travel 4,000 miles to address the Iskra board, so it can consider what should happen to Bauman. Lenin refuses to see Miliutin. Zasulich is outraged, and storms out. Lenin tries to end the meeting, but Martov demands an inquiry into Bauman's behaviour. Lenin refuses on the grounds that Bauman's exemplary work for the party should not be threatened by his personal misdemeanours. Martov argues that party and personal morality cannot be separated, and is upset by Lenin's derisive response.

Lenin falls deliriously ill with shingles, but in order to stop Martov taking charge travels to see Plekhanov and persuades him to support his rules for party membership at the coming congress.

Later, the Social Democrat Congress convenes in Brussels, and discusses the possible expulsion of the Jewish Bund for refusing to give over control of their organisation to the party. The vote is deferred, and as police are on the way to break up the meeting, the Congress agrees to reconvene four days later in London.

London. The debate is now about the rules that will determine the membership of the party in the future. Martov argues that Lenin's formula will rule out too many useful members of the party, but Lenin is convinced that the revolutionary movement must be controlled by a vanguard party lead from the centre. Martov wins the vote, with the support of the Jewish Bund. Martov is then barred from a secret caucus called by Lenin, but still manages to confront him afterwards. Lenin reveals that the party will vote on the Bund's expulsion the following day, and he expects Martov to vote for that expulsion rather than opportunistically support the Bund because he needs their vote. Martov accuses Lenin of being another Robespierre.

The next day, the Bund is expelled, and so Martov now leads the minority. Lenin proposes that the Iskra board be reduced to three members - himself, Plekhanov, and Martov - removing Zasulich and Axelrod. Zasulich erupts and calls Lenin a tsar, before storming out of the debating chamber, swiftly followed by Martov and Trotsky.

A few days later, the party gathers at the grave of Karl Marx. Trotsky informs Lenin that he did what he had to do. Lenin chides him, and says that until he realises the party is above everything else history will have no use for him. Martov walks away without speaking. Lenin and Krupskaya stroll through the cemetery, while back in Russia, the Tsar shoots at crows, but does not seem to be hitting any of them.