The opening book in Len Deighton's Game, Set, Match series!
Brahms Four is the best East German source the British ever had, but now he thinks his cover has been blown—and he desperately wants to come over the Wall and escape from Berlin before he's exposed. There is only one person he still trusts, British agent Bernard Samson of the SIS (Secret Intelligence Service). So Samson, who retired to a desk job five years before, is thrown back into the field. But but before he can even set out on his mission to help Brahms Four, he realizes there's a traitor very close to him. He must find out who it is...and get Brahms to the West before it's too late.