The usage of the polygraph in "The Good Soldier" is very unsettling and leaves a multitude of questions that need to be answered. The first major, and perhaps most important, polygraph incident is Saul flubbing the first test when asked whether he slipped razor. This could indicate a lot of things. The most obvious would be Saul as the mole. But if he were truly this good of a mole, would he have failed so easily the first time and passed the second? Then again, if he was the mole, he did get away unscathed. Another thought is that the writers used Saul as a benchmark before Brody's test, to show that the test can go in any which direction depending on the disposition of the subject. If Saul can have different answers at different times with different results, then so can Brody.
Carrie and Brody hook up in the episode, and it's fairly interesting. They seem completely at ease with each other, and Brody certainly has no problem performing with Carrie as he does with Jessica. Carrie's behavior stays consistent, though. She's able to instantly disconnect from the sex, using it as a tool. It seems like she blew her cover at the end of the episode, asking about Brody cheating on his wife, leading to Brody telling her to get in his car at the end of the episode. Will he know?
Despite Brody passing the test, all signs still point to him being a sleeper. We're reminded during the service for Walker that Brody, in fact, beat Walker to death. Then, Brody gets through the polygraph--including the question about cheating on his wife which he obviously just did with Carrie.
The people outside of Carie's immediate life continue to have short lifespans. Faisel and Aileen have barely been introduced and now Faisel is dead, killed by their handlers. We get to see how scared Faisel is and how Aileen was the original terrorist, but not enough time was spent on them to really build anything. Still, I'm not sure I would like more time spent on these other plots. Carrie being the central pillar of the show works very, very well, and disruption to that may not beneficial.