With the help of a few old allies and contacts, Smiley manages to unmask and capture a Soviet mole by the end of Tinker, Tailor, Soldier, Spy. Doesn't sound that impressive, until you remember that he's officially retired from the Circus for most of the novel, and thus technically a civilian. Not only does he manage to get his old job back, he manages to get himself appointed Chief of the same intelligence agency that kicked him out, and he does it without ever throwing a punch or firing a bullet. As a colleague later remarks, "Only George Smiley could get himself appointed captain of a sinking ship".
Karla's first meeting with George Smiley, which cements him as a Worthy Opponent to end all Worthy Opponents. Smiley has him cornered in a sweltering Indian jail after the Circus has already successfully blown his communication network in California, and he has nothing left to do but wait for the plane back to Moscow—where everyone fully expects him to be executed on the spot for his failure. In his entire career, Smiley never meets another agent with as much reason to defect as Karla. Not only does he not defect, he never says a word, he barely moves, and he doesn't even sweat. Smiley is so rattled by his silence that he doesn't protest when Karla quietly snatches his cigarette lighter as the guards are escorting him away. Just a few short years later, Karla is in charge of Moscow Centre, and he comes dangerously close to bringing down British Intelligence...with a cigarette lighter.
In the third act of The Honourable Schoolboy, Jerry Westerby goes to Cambodia to track down a smuggler pilot who might know the truth about Karla's plans in Hong Kong. It would be a simple assignment, if not for the fact that the Cambodian Civil War is going at full speed, and the countryside is crawling with murder-happy Khmer Rouge militants. Despite being stuck in a besieged war zone with no way out, Westerby manages to find his man, climaxing with a scene where he interrogates the guy as he's flying him over a raging battle in the jungle below in a rickety plane while strung out on opium. Say what you will about Westerby's ego, but the man has balls of steel.