Monday night’s episode of the ABC crime series “Castle,” the second of its fourth season, signified a return to the show’s winning, quirky formula after the near-stumble of its season premiere. I’ve praised “Castle” in the past, and though its third season’s finale gave cause for worry, the series’ most recent episodes provide an object lesson in entertainment programming, especially for genre writers.

For those who haven’t seen the series, “Castle” is a semi-comic police procedural about a bestselling mystery author, Richard Castle, who finds himself partnered up with a beautiful female police detective in Manhattan, Kate Beckett, to help solve crimes. The implausible premise is no impediment to enjoying the show, as its stars Nathan Fillion and Stana Katic are both a delight to watch as the central characters; their skill as performers is evident and easy to appreciate.

In addition, and even more importantly, the gaudy premise matches the show’s narrative style; it is a throwback to the great tradition of American surrealistic mysteries of the 1930s and ’40s. That’s a very important—and, alas, currently underappreciated—trend in mystery fiction exemplified by the writings of Ellery Queen (the truest master off the form), Fredric Brown, Anthony Boucher, Craig Rice, Hake Talbot, Joel Townsley Rogers, Herbert Brean, and the other great master of the form, John Dickson Carr (and these writers all owe a debt of gratitude to the earlier British crime fiction of G. K. Chesterton, the American Jacques Futrelle, and a few others).

What these and their contemporaries excelled at was creating a sense of wonder, building a fantastic situation that has an inexorable logic of its own. In their way, they conveyed a sense of American life as a realm of astonishing possibilities ultimately grounded in common sense, logic and morality. It’s a form of fiction I enjoy greatly and which I think has much to recommend it.

“Castle” exists in that tradition. A typical episode will begin with a bizarre murder, then progress to the investigation of a series of quirky or downright bizarre suspects, witnesses, and clues while the two lead characters work out matters from their personal lives and their powerful but largely unspoken attraction to each other. It’s great fun, although the events of the show are serious and often have important implications.

Last season’s finale cliffhanger, however, went in a more overtly suspenseful and dark direction, ending with Beckett shot by a sniper as she spoke at her former boss’s funeral. It was much more like an episode of “24″ than “Castle” viewers would expect. And this season’s opening episode was much darker in tone than the usual. As Beckett recovered from her grave  injuries and the detectives investigate the attempt on her life, she and most of the other  major characters were upset with Castle for various reasons. He, too, was down in the dumps, concerned that failing to declare his love for Beckett could have made a difference in their lives.

All of this angst came off as very 1950s-Ellery Queen in approach, but that decade, alas, was not a good one for Queen.

Although the cliffhanger episode and the season opener were interesting and quite watchable, neither played to the show’s strengths.  Fortunately, last night’s episode marks a solid return to the program’s basic formula. The murders are committed by a costumed superhero who carries a samurai sword with which he cleaves a would-be rapist literally in half, from head to, well, groin.

That may sound very modern (in its spectacular grossness), but in fact it’s the kind of thing one often finds in novels by Queen, S. S. Van Diane, and others. It’s crazy but just barely possible, enough to keep you from throwing the book at the wall (for me, at least). And the scenes surrounding the murder in this “Castle” episode are handled without excessive gore– in fact, rather comically, as a morgue sequence shows two adjacent body bags holding the two halves of the body.

Castle and his daughter also work out their problems, which had left her bitter towards him in the previous week’s episode. The episode also includes some interesting background information on the world of comic book fiction, fizzy dialogue between Castle and Beckett, and several goofy suspects with weird personalities and nutty motives.

In addition, it is revealed—though not to Castle—that Beckett was indeed still conscious when he told her he loved her as she lay presumably dying at the end of the previous season’s cliffhanger episode. It’s a very good plot development which holds promise for much irony and emotional dueling in future episodes.

So, what’s the lesson here for genre writers and admirers alike? It’s all right to wander outside the boundaries once in a while, but the boundaries are there for a reason: because the conventions of any particular genre work. They come into being, after all, because people literally buy the narratives that take on that form. And I would posit that people like these narrative conventions because they speak the truth to them in a pleasing way.

“Castle” does this too—and that, I believe, is what makes it both popular and deserving of its success.

Certainly Castle has plenty of immorality and other damaging personal behavior in evidence. Set in modern-day Manhattan, the series stars Nathan Fillion (Firefly) as wealthy mystery writer Richard Castle, who accompanies police detective Kate Beckett (Stana Katic, The Spirit, Quantum of Solace) on homicide investigations in order to glean valuable real-life knowledge to use in his murder mysteries. The conceit is that Castle is able to get this kind of access because he is a friend of the mayor and many other highly influential people in the city.

This cute premise enables the show to give viewers a view of Manhattan high life while ensuring its central characters are doing something highly worthwhile: bringing murderers to justice, of course. That has been a staple of mystery fiction dating back to the nineteenth century and exemplified by MGM’s highly enjoyable Thin Man film series of the 1930s and ’40s and the TV series Hart to Hart, Remington Steele, and McMillan and Wife. And in presenting the stories and circumstances behind the murder mysteries the couple is engaged in solving, Castle has plenty of opportunities to show the great variety of vices in New York City life both high and low.

The show’s overall approach thus fits right in with the contemporary trend of using sensationalistic subject matter and depictions of immoral, selfish, or irresponsible behavior to tell stories that make positive moral points.

This approach is evident in the characterizations of the people surrounding the title character. Castle’s mother, former Broadway star Martha Rodgers (superbly portrayed by Susan Sullivan) and his first ex-wife, Meredith (Darby Stanchfield), embody irresponsibility and selfishness, while Det. Beckett and Alexis, Castle’s daughter, represent good sense and altruism.

Katic portrays Beckett as a stolid, earnest, determined police detective with the attractiveness of a supermodel. (Yes, this is a Hollywood product.) A particularly laudable aspect of the show is how it portrays Alexis’s desire to be good while surrounded by temptations as she grows up wealthy in Manhattan; actress Molly Quinn conveys those stresses superbly.

Castle stands between those two pairs of women both literally and figuratively; he is no monk, and he is habitually given to much mockery and high spirits, but he is highly successful (and maintains an amazingly expansive Manhattan apartment) because he works hard and is one of the best in the world at what he does. While wealthy and privileged, he is occasionally taken down a peg or two, especially by Det. Beckett.

Castle, moreover, is often a slave to his desires (like human beings in general). In “Always Buy Retail” he excuses a choice he regrets by saying, “The thing with crazy people is: the sex is terrific!” Yet he is a very understanding and loving father to Alexis, and is more than willing to disregard his own safety in order to help Kate and the various crime victims he runs across.

In the pilot episode, “Flowers for Your Grave,” Castle is presented as an annoying, wealthy, over-privileged smart-aleck, but in subsequent episodes the producers immediately toned down those unappealing qualities and showed him to be a willing learner in his role of following police investigations, and, more importantly, they stressed his positive qualities as a responsible and loving father to well-bred Alexis, whom he is raising as a single parent.

On the job as a consultant to the NYPD and Kate Beckett in particular, he shows great insights into people’s character and human nature in general, and typically at some point late in each episode he will convey some wise piece of character analysis that points the way toward the solution of the mystery at the center of the story.

Thus Castle is a reasonably complex character and exemplifies the show’s approach. The overall impression the program sends is that life is not easy, but it still can and should be filled with joy. That’s a rather stark contrast to much of what is conveyed by the contemporary American culture, and the way that Castle melds that optimistic, positive spirit with strong moral messages is exemplary.

For example, episode 3, “Hedge Fund Homeboys” depicts a group of modern-day “vile bodies,” a group of spoiled, privileged prep school teens, among whom a sexual triangle leads to premeditated murder. The self-confidence and smugness of the murderer are clearly a consequence of a spoiled upbringing, and he is a thoroughly unlikeable character–there’s no sympathy for the devil here.

That’s especially true because of the way Alexis dispels any potential cynicism in the episode and removes any excuses for the teens’ transgressions (such as blaming the parents or the culture), for she is not only well-behaved and morally astute, she has a powerful and active conscience. In a very affecting scene, she is wracked with guilt and insists that her father discipline her for a minor offense she had concealed from him until the guilt overpowered her and she felt compelled to confess.

Her earnestness about wanting to do the right thing is laudable and appealing. Even more importantly, her intentionality in making moral choices makes a strong case that people can and should be held responsible for their actions.

This idea is presented with similar force in episode 4, ‘Nanny McDead.’ A wealthy man who has been cheating on his wife with at least two different women causes a murder, as one of his mistresses kills the other out of rage when she finds out about this further betrayal. She is pregnant and had believed him when he told her he was planning to leave his wife and marry her. After talking her out of committing suicide, Kate discusses the husband’s role in the murder: “What that guy did had consequences, only he’ll get to just walk away,” she says.

That’s true, and it vividly shows the awful consequences of adultery and the overweening selfishness it represents. The man’s adultery led directly not only to divorce but also to murder, and Beckett and the episode’s writers are careful to make sure we understand his full culpability. The combination of lust, anger, murder, and accurate attribution of moral responsibility makes for a powerfully moral story without any hint of preachiness.

The same is true of episode 7, “Home Is Where the Heart Stops.” Beckett tells the grieving daughter of the murder victim, who feels guilty for not being with her mother when murder occurred, “I’m telling you it’s not your fault. The ones to blame are the monsters that murdered your mother.” The series is full of such moments.

While presenting a good deal of sensationalistic subject matter, Castle does right by its viewers in refusing to give in to moral relativism or make vice and selfishness glamorous. It’s exemplary series television.

—S. T. Karnick, editor of The American Culture