On 20 August, the Presidium of the Czech Communist Party discusses recent negotiations with the Soviet Union. Brezhnev's regime is alarmed by Alexander Dubcek's mixture of democracy and socialism during the 'Prague Spring'. That night the Soviet Union invades, an action described as 'fraternal assistance'.

Dubcek's reforms are supported by Cernik, Kriegel and Smrkovsky, and opposed by Kolder, provincial boss Bilak and Presidium Secretary Indra. All agree that they cannot make an armed response against fellow Communists. Outside, a child is shot dead by Soviet troops. At 3.30am, soldiers enter Dubcek's office and place everyone under 'protective custody'. In the morning, Dubcek and supporters, including Kriegel and Smrkovsky, are taken away. A factory siren announces a strike in protest at the occupation. At 10pm, Mlynar and the remaining office captives are released. Dubcek, Cernik, Kriegel and Smrkovsky are held at various KGB posts. Smrkovsky fears he is to be killed. The 14th Congress, held in secret with 1,100 delegates, supports Dubcek.

At the Soviet embassy, Party members including Mlynar meet the Soviet ambassador, who suggests that they form a new Government rather than wait for Dubcek. Most agree, with Bilak replacing Dubcek. However, on 22 August, President Svoboda refuses his consent. He flies to Moscow to talk with Brezhnev. Dubcek is called to Moscow, and insists that his colleagues are brought for negotiations.

By 25 August, the Soviet Union has failed to set up a collaborationist government in Prague or to break Dubcek or Svoboda in Moscow, and Indra's revolutionary tribunal has been abandoned. Presidium members gather at the Kremlin. Dubcek collapsed soon after his arrival and is ill. Mlynar informs him of his popular support. Mlynar learns that, before his arrival, the delegation agreed to annul the 14th Congress. Vice President Husak argues that popular support is irrelevant, as the Soviets will not leave until Czechoslovakia is normalised. Mlynar argues that, since the Soviets have been forced to negotiate, the delegation should call for troop withdrawal and the continuation of reforms. Bilak asks whether Mlynar wants civil war.

Mlynar drafts a statement which is partly critical of the Prague Spring while denying that it was counter-revolutionary, and which does not legitimise the invasion but empathises with the Soviets' perceived need to invade. Dismissing this statement as provocation, the Soviets propose a text justifying military intervention to prevent counter-revolution, maintaining the occupation and purging reformers. The delegates, realising that signing this draft will betray the Prague Spring, painstakingly achieve tiny changes, but Mlynar observes that this makes them co-authors of their own destruction.

The delegates agree to sign, to avoid bloodshed and to return to their families. They argue with Mlynar, who refuses to sign as a matter of integrity. Smrkovsky insists that, given collective responsibility, the delegates could still achieve reforms, which was preferable to the military government that would take over if they refused to sign. Mlynar agrees to sign. Kriegel arrives, and refuses to sign; having been brought as a prisoner, he tells the others that they are fooling themselves.

At the signing ceremony, Brezhnev regrets being forced to invade. Dubcek insists that his reforms would strengthen socialism, which disappoints Brezhnev, who notes that even he must refer policy documents. Czechoslovakia belongs to the Soviet Union, as the United States acknowledged two days before the invasion while agreeing not to intervene. Dubcek will not sign. Brezhnev storms out. Svoboda apologises and they meet again later. Dubcek refuses to sign, but signs after being sedated. Both sides shake hands. Nobody speaks on the plane back to Prague.

The Party annulled the Congress, reintroduced censorship, banned opposition groups and abandoned reform. The soldiers' presence became permanent. Dubcek was removed in April 1969, and Kriegel and Smrkovsky were expelled and have since died. Bilak became the party's ideologist, Cernik denounced Dubcek, Husak took over from Dubcek, expelled half a million of his supporters and became President in 1975. Mlynar resigned two months after the negotiations, organised Charter 77 and has since emigrated to Vienna.

Six years after the negotiations, Dubcek and his wife attend the theatre on a rare outing while under house arrest. Fellow audience members give them a passionate ovation.