And a show that has always tended toward the downbeat has been even more bleak than usual. In the first two weeks, pragmatic but questionable decisions by cops have led to the deaths of an old man and a young boy. Adams has lied to a rape victim to trick him into admitting he’d been raped; Officer John Cooper (Michael Cudlitz), the show’s moral bellwether, has been forced to shoot a man in the back when a traffic stop went bad. One character’s mother has died; another’s lover has left him.

“Southland” is not a perfect show, by any means, and sometimes it balances its gloominess with epiphanies that are undeniably pat, if not excessively heavy-handed by the standards of basic cable. As the seasons have passed, its lapses into preachiness and formulaic plotting have increased. Weaving two or three seemingly everyday story lines into a satisfying narrative every episode is a delicate trick, and when it doesn’t work, you’re left with something that feels inconsequential. The temptation to resort to proven dramatic and emotional strategies — that is, melodrama — must be strong.

But “Southland” still gets it right most of the time, and stands above the more popular police and forensic dramas that satisfy our appetite for predictability while insulting our intelligences to greater or lesser degrees. It acknowledges the arbitrary, contingent, inexplicable nature of human behavior in the way its stories circle and lurch and stop midstream, and in the way it crowds the frame with unnamed cops and masses of angry or bored or hyped-up bystanders. It pays attention to everyday conversation, and disdains the haiku of superhuman detection and analysis that substitutes for dialogue and action on other shows.

Most important, it does right by its actors, many of whom are better on “Southland” than they’ve been elsewhere. Ms. King and Mr. Cudlitz have been exemplary since Season 1, and Dorian Missick, as Adams’s remarkably levelheaded partner, has been their equal since he joined in Season 4.

Like most cop shows, “Southland” posits a daily face-off between idealism and cynicism that’s probably pretty far removed from anything a typical police officer confronts. But it keeps the line between them fuzzy. When Cooper’s new partner has a meltdown in the line of duty and says, “You have to be crazy to want this job,” there’s no speech or lecture in reply. Cooper just murmurs, “You don’t have to convince me,” and walks away.