This is book number 4 in the George Smiley series.
When word reaches The Department an ailing section of British military intelligence that Soviet missiles are being installed close to the West German border, it seems the perfect opportunity to show Control and Smiley, their rivals over at the Circus, that The Department still has value.
Former spy Fred Leiser is lured back from retirement to investigate, and manages to cross the border into East Germany in a dangerous nighttime operation. But the world has changed since The Department's glory days during the Second World War. The harsh realities of the Cold War now prevail, and there is no place for heroes.