Lubyanka, the FSB headquarters in Moscow
More from this series
Martin Sixsmith gets under the skin of the fastest growing and arguably most politically influential secret service in the world the "new KGB".
In Programme Two, we look at the organisation's current position and methodology.
The murder of Alexander Litvinenko was only the latest in what many believe were a succession of recent, FSB-ordered or inspired liquidations of political enemies of the Kremlin.
Anna Politkovskaya, Russia's best-known investigative reporter and Putin critic, had survived poisoning before being shot dead outside her flat. It was Vladimir Putin's birthday.
FSB insiders tell us that even if such killings are not sanctioned from the top, the system of patronage means that the killings may be undertaken "freelance" by junior agents seeking to please those higher up.
Who else might yet become an FSB target? We hear from Boris Berezovsky, the former oligarch and émigré seen by many as the Kremlin's most hated adversary.
To what extent is it government, and to what extent is it the shady links between politics and big business in Russia that are driving the FSB's operations? And just how central is the FSB to Russia's reviving ambition to be regarded as a global superpower?
Beyond the suspicions, we will also ask to what extent the FSB has become the guiding hand behind the new political order in Russia. Is it an engine of the state, or does it operate above and beyond it?
Finally we assess what its resurgence says about Russians' willingness or desire to move on from their Soviet heritage.