There are few things more difficult in television than properly handling the "big moment" — the evolutionary tipping point of a series that fans have been waiting to see and critics have been waiting to judge.

There are few things more difficult in television than properly handling the "big moment" — the evolutionary tipping point of a series that fans have been waiting to see and critics have been waiting to judge.

These can include life or death moments, innocent or guilty moments, win or lose moments, which-one-will-be-chosen moments and, of course, will-the-motorcycle-reach-the-down-ramp-without-falling-into-the-shark-tank moments.

But no "big moment" carries as much weight as the commitment decision. Will two characters we've grown fond of as they've drawn closer realize their need for each other ... and, more importantly, what happens after that?

On Monday, it's apparently time for the "big moment" on "Castle" — ABC's lighthearted procedural that has kept mystery writer Richard Castle (Nathan Fillion) and his crime-solving muse, Detective Kate Beckett (Stana Katic), playing their own version of "Will they or won't they?" for four seasons.

It's a difficult dance to do right, but "Castle" has pulled it off to this point by tugging at the heartstrings with (almost) perfect timing. Monday's season finale promises to be the point of no return for Castle and Beckett — who this season have seen two close-to-home couples disintergrate, and a third get married.

"Castle" has maneuvered through this minefield by shadowing the progress in the relationship within the nature of the weekly mysteries. One of the show's best hours was this season's "Cuffed" — which teasingly opened with the duo in the dark (figuratively) on a mattress (literally), only to discover they'd been drugged and kidnapped, and have no immediate memory of how it happened.

They were not only forced to work together to escape the jam (which, eventually, would include a hungry, rare tiger in the next room), they were forced to accept those things that drive them up the wall. He's not a physical enough presence to steady her on his shoulders; he can't help but wonder how she can chase criminals in high-heeled boots.

"Castle" works best in these moments. We know the killer will eventually be caught; what fans need to see is whether he brings in her morning coffee and she allows him to speculate (as he did this past week) whether the deceased was dispatched by an actual zombie.

The zombies, naturally, provided yet another metaphoric clue to their eventual coupling. Beckett, shut down emotionally after a near-death experience at the end of last season, understood the need to be among the walking dead and let Castle be there for her.

He, in turn, finally got past his hurt at being shut out since professing his love to a bleeding Beckett after she had been shot near the heart. And fans, meanwhile, breathed a huge sigh of relief.

That last wall between them had been constructed too artificially, at least as far as credibility can go in a show such as this. Castle's too smart not to have releazed what Beckett was going through.

It took a verbal slap upside the head this week from his mother (the wonderful Susan Sullivan) and a few well-timed games of laser tag with his daughter to prod his ego out of the way.

Which brings us to Monday's moment, and how will it be handled. This is tricky stuff in televisionland; handled poorly, the fragile chemistry on which a show is built can evaporate in an instant.

The shows for which this sort of thing works have a strong enough secondary thread to keep things going. For instance, see Buffy and Angel (and eventually Spike) in "Buffy the Vampire Slayer." The romantic entanglement enhanced the drama.

Such is not always the case. Some call it "The Moonlighting Curse," as when Maggie and Dave finally did the dirty deed to satisfy the frustration of viewers everywhere ... and immediately left the show with nowhere else to go.

"Moonlighting" is not alone. "Cheers" never did resolve its Sam and Diane tortured affair to any degree of common sense. Nils pined for Daphne for a decade, and the air went out of their "Frasier" storyline once they became a couple. Maggie and Joel flirted for so long on "Northern Exposure" that their eventual roll in the hay didn't satisfy anyone.

"Friends" had some fun with the Ross and Rachel possibilities, but in the end there was nowhere else for them to go but to each other; while the comedy hit high notes as Chandler and Monica courted — only to lose steam after a memorable proposal.

Heck, even Lou Grant shared a date (and a kiss!) with Mary Richards, if only to wind up laughing in the middle of it.

"Castle," though, should look for inspiration to the current series it most closely resembles — "Bones," the Fox procedural about a dysfunctional, murder-solving duo.

A year after Brennan (Emily Deschenal) told Booth (David Boneraz) that they couldn't be a couple, the death of a friend brought them together in scenes unseen in the season finale. At which stage, she informed him in her trademark perfunctory style: "I'm pregnant. You're the father."

It was short and sweet and, given the nature of their relationship, perfect.

This season, Bones, Booth and company have gone about solving grisly murders and awaiting the birth of the child; who arrived — in a barn, after the couple was turned away at an inn — following a discussion of the need for a religious upbringing.

And with that,"Bones" continued on its oddly merry way. The show survived the "big moment" by not dealing with it at all, allowing its characters to continue being who they were.

It's a lesson, and a question, that hangs over "Castle." Now that they've gotten here, do they have anywhere else to go?

Mail Tribune news editor Robert Galvin writes the occasional column about television for Tempo. He won't next week, because he'll be on vacation. he can be reached at