This episode is about unrequited love in its various extremes - from arsonist Travis Owens pathological love for Laura Smith; to Evan's rekindled strained relationship with Cassidy; to Nash's undiscovered love for Caitlin. Indeed, an arsonist is needed to put the spark in these relationships, because they are far apart in circumstance. Certainly Nash and Caitlin are so far apart that the writerly device of a divine angel is needed to bring them together.
The wonderfully scruffy character actor Tracy Walter plays Angel, who first appeared in "Hit Parade," episode 18 from Season 2. Angel was also there for the significant episode "Revelations," episode 39 from Season 3, in which Angel helps a hurting Nash come to terms with his lost brother Bobby. Angel gives Nash the impossible clues to figure out his deeply personal anxieties which no one could possibly know (those that not even Nash can admit to himself). In the case of Caitlin Cross, any positive relationship remains remote because of the fact she is Internal Affairs. She is out to get Nash and his SIU team, and that makes any forward motion impossible. Even though the spark is ignited by Angel, Nash keeps his distance. (She decides to lighten her case against Evan and recommend a reprimand.) This spark may continue to smolder until the end of the season before anything happens, but they do maintain a tight eyelock at the end of the episode. This, and the kiss in "Swingers," episode 61 confirm the attraction between Nash and Caitlin, but it's going to be a bumpy road, as Caitlin hisses at Nash "I hate you!"
Evan's case of brutality seems entirely justified, given the fierce resistance put up by the panicked arsonist. How can this even compare to Nash's torture dunking of a prisoner last week? Evan was attempting to apprehend a suspect. Nash's suspect was already safely in custody (apparently knocking the guy out with his pistol wasn't enough for Nash) - Nash's violation is egregious, a gross civil rights violation. The fact that Caitlin participated in the dunking nullifies her investigation, but there's a hypocritical double standard against poor Evan. It's another case of NASH BRIDGES smoothing over those kinds of pesky legalities...
For more, see synopsis for Episode 63