The final episode tells the inside story of two relationships - Barack Obama's campaign to win over Russian president Dmitry Medvedev, and Medvedev's own complex dealings with Vladimir Putin.

Obama became president determined to rid the world of nuclear weapons. To begin the process he needed Russian help. So he set out to reset relations with Russia. Ignoring Putin, whom many considered still in charge, he concentrated on Medvedev.

Top officials on both sides take viewers deep inside the negotiations. They describe how a phone call between the two young lawyer-presidents finally clinched the agreement - which cut their countries' nuclear arsenals in half.

But inside Russia, Medvedev had a harder time. He responded to the 2008 global financial crisis by setting out to turn Russia into a modern democratic economy. He made little progress. He told Obama that Russia's most famous dissident, Mikhail Khodorkovsky, would get a fair trial. It did not happen.

In the end, Medvedev stepped aside and nominated Putin to be their party's presidential candidate for the 2012 election. Top Kremlin insiders, including Medvedev and Putin, tell how the deal was done - and how it set in train a process that made Vladimir Putin look vulnerable for the first time. Show less