In the novel, Leamas is a good spy, he gets results, but he has a fatal flaw that is present from early on in the novel; he possesses humanity - it is just very well obscured behind a well constructed, yet slowly crumbling wall. One of the first glimpses we get of Leamas" well hidden humanity is when he is conversing with Control about Riemeck. Control questions him about the emotions he experienced due to the loss of his last agent.
""We have to live without sympathy, don't we? That's impossible of course one can't be out in the cold all the time; one has to come in from the cold d"you see what I mean?" Leamus saw. He saw the long road outside Rotterdam, the long straight road beside the dunes, and the stream of refugees moving along it; saw the little aeroplane miles away, the procession stop and look towards it; and the plane coming in, nearly over the dunes; saw the chaos, the meaningless hell, as the bombs hit the road. "I can't talk like this, Control."" (Page 18).
The vivid image Leamas is recalling shows the reader the horrors that he has witnessed during his service, and that he hasn't been able to completely shut them out. He has been able to shield their impact from himself, but it is still there, churning beneath the surface. Leamas tells Control that he can't talk about what he felt when Riemeck was killed. He has no way of expressing his feelings because he has hidden them for so long that he is almost incapable of vocalising and expressing emotion. This also shows us how fragile the wall between his emotions and his consciousness is at this point.
An example of Leamus" inability to be completely detached is the trust that he placed in Control and the organisation. He was forced to have this exceptional amount of trust and respect, both in the cause that they were fighting for and the organisation itself; because it was for this cause that he was sacrificing his emotions and humanity.