In John Le Carre's The Spy Who Came in From the Cold, how does the protagonist's relationship with Liz help him 'come in from the cold?'

Alec Leamas, the protagonist of John Le Carre's seminal Cold War espionage novel The Spy Who Came in From the Cold, is a burned-out field operative for the British foreign intelligence service, popularly known as MI6. As the novel begins, Leamas is waiting patiently at a checkpoint in divided-Berlin for an agent, an East German he has meticulously recruited to spy for the West. As Leamas waits, the reader is informed that this agent's life is in grave danger, and that other East Germans that spied for the West have already been captured, with the insinuation of torture and death that would inevitably follow, and that there is, in Leamas' line of work, a very thin line between life and death. 

After the agent for whom Leamas was waiting at the checkpoint in Berlin is killed attempting his escape, the emotionally-exhausted British operative returns to London and to the headquarters of the agency for which he works. It is during Leamas' meeting with the director of MI6, known in the novel as "Control," that the meaning of the book's title becomes clear. Explaining the extremes to which Western intelligence agencies must go in defense of liberty against a relentless and ruthless adversary, Control ruminates upon the psychological toll such work takes upon its most dedicated practitioners:

"We have to live without sympathy, don't we. That's impossible of course. We act it to one another, all this hardness; but we aren't like that, really, I mean . . . one can't be out in the cold all the time . . . one has to come in from the cold . . ."

As Control and Leamas continue their discussion, with the latter rejecting the former's apparently insincere invitation to his subordinate to accept a less demanding office job, Control once again dispatches his agent into the field--back out into the cold. 

The character of Liz, the young naive communist, is a plot contrivance. She exists to humanize Leamas, and to represent the innocence of those who live outside the confines of the intelligence game at which Leamas has become a master. The student's question--how does Liz help Leamas come in from the cold--is, consequently, something of a misnomer. Liz is, unknowingly, an integral part of Control's plan to eliminate a skilled and deadly East German intelligence officer whose guile has resulted in the decimation of Leamas' network of agents. She believes that she is helping this older, rumpled, thoroughly disillusioned man to exist in a more peaceable and just society. In reality, she is being used by Control and by Leamas to exact revenge on their nemesis across the 'iron curtain.' Not only is Liz not facilitating Leamas' transition from one world to another, she is, in fact, being pulled into a game from which she will not return. Leamas's relationship with Liz exists entirely within the context of his return to 'the cold.'