First off, I have to apologize for the late review. Life interfered with my television viewing and it's a shame, because this week's episode was very interesting in a way that will have repercussions on the relationship between Foster and Lightman—and probably not in the direction hoped for by many of the show's fans. The story is an intricate game of crossed loyalties, stressed loyalties and ultimately, competing loyalties, as we find out just how far Lightman will go to support a partner—though oddly, not his own partner.
The central theme of "Dirty Loyal" is summed up in a question an Internal Affairs officer asks Cal: "Is this about finding a corrupt cop for you or is this about saving your friend?" The writers have already explored the practical limitations of Cal's science, in that it is not a hard science and there's about a thirty percent margin for error even with someone as skilled as Cal. "Dirty Loyal" takes the margin for error a step further and asks what happens when Cal's own motivations play into how he applies his science. The answer is not one that sits comfortably with Foster and, I suspect, with many members of the audience. I think the writers have taken a brave step in showing us Lightman's flaws may extend to his character—but it's a step that must have repercussions in later episodes for it to pay off. Lightman and Foster end up in a place by the end of "Dirty Loyal" that can't be gone back on, because an exploration of corruption has gone hand in hand with the exploration of loyalty.
The story's set up has Internal Affairs contacting Foster to show her a tape of Detective Wallowsky and her partner, Detective Farr, in which Farr is visciously beating a young gang member. The Internal Affairs officer knows Lightman is romantically involved with Wallowsky and want him to stay out of the investigation into the beating. Gilian is unhappy at Cal's personal involvement with a possibly dirty cop and wants him to take a step back. Cal's reaction, however, is to go to Wallowsky and confirm for the audience he is indeed involved with her. Cal is upset she won't ask him for help in the investigation, and we are left to wonder at both characters' motives.