"I was a happy man back then," Noah  explains. "Was proud of my family. My first book had just come out. Everything I'd promised myself I would achieve as a young man, I'd done it."

"But?" he's asked.

And Noah replies, "That's the thing: There is no 'but.' When I look back, I can't tell you why it happened."

"It" is the subject of "The Affair," the new drama premiering Sunday at 10 on Showtime, and the most complicated and interesting thing the show does is to make it clear that there was no obvious explanation for Noah cheating on his wife. Sometimes, affairs happen because partners aren't getting along, because one of them has a weakness the other can't help with, or because one partner just got bored with the other.

Sometimes, though, they just happen.

"The Affair" offers a little from Column A, a little from Column B. Noah (Dominic West) is, as he says above, happily married to Helen (Maura Tierney). Their life together isn't perfect — their four kids fight with each other, his debut novel wasn't as successful as he had hoped, and her rich and famous author father(*) looks down his nose at him — but it's good enough, and the pilot episode goes out of its way to make clear this is not a marriage gone stale over time. On the other hand, his mistress-to-be Alison (Ruth Wilson) has a recent tragedy in her past that has altered her marriage to Cole (Joshua Jackson). In a reversal of classic adultery tropes, the two of them still connect sexually, but emotionally there's a gap between them as vast as the ocean that's just a few steps away from their old house on the beach.

(*) The father-in-law is played by West's fellow "Wire" alum John Doman, and now I hope that the two keep this double act going for years to come, with Doman somehow always playing an authority figure who disapproves of West, even if he's not always as blunt and profane in expressing that disapproval as Bill Rawls was to McNulty.  

Created by Sarah Treem and Hagai Levi — he created the Israeli show that inspired HBO's "In Treatment," while she wrote for some of the best "In Treatment" characters (gymnast Sophie in season 1, cancer patient April in season 2, troubled teen Jesse in season 3) — "The Affair" tries to tackle Noah and Alison's relationship from several angles at once.

The series is presented "Rashomon"-style, with some scenes presented from his perspective, and then shown again from hers. (The pilot episode splits things evenly, with the first half Noah's POV and the second half Alison's; Treem says that the device will be used in a less straight-forward manner.) Beyond that, we see that both characters are revisiting this period from a time a few years in the future, when each is being interviewed by a police detective for reasons unknown.

So the present-day scenes are complicated not only by matters of perspective, but memory. When Noah and Alison first meet at the Hamptons restaurant where she waits tables, for instance, his clothes are nicer in her account than his, while she's very well put together in his recollection and washed-out and unglamorous in hers. As he recalls it, she was the aggressor in the relationship, while she sees things very differently.

It's in the way that Treem and others use that shift in perspective, more than anything else, that makes me wish Showtime had made more than one episode available before Sunday's premiere. (The first episode is already available On Demand and on YouTube, while Showtime says that because the series was filmed out of sequence — all beach scenes together, then all scenes with one family, then the other, etc. — critics won't be able to see additional episodes until next week.) The pilot doesn't spend too much time showing you the same scenes twice, but when it does, the differences tend to be very binary in the He Said, She Said of it, where everything's exactly the opposite depending on who is telling the story. And that works fine for a pilot that has to tell you how to watch the series, but it also seems like something that could get old in a hurry if the different accounts don't get more complicated.

Fortunately, the show has four strong actors at its core. West and Wilson are more prominent in the pilot than their co-stars — Tierney is mainly there to give you a sense of the solid foundation of Noah and Helen's marriage, while Jackson is there to suggest the opposite for Alison and Cole — but if you want charismatic, nuanced performers who can carry you through a long and winding story in which their characters cheat on their spouses, it's hard to ask for better than those two.

The pilot episode also does an excellent job of making each marriage feel lived-in, even if one is, on paper, stronger than the other. We spend a good deal of time just watching Noah and Helen trying to pack the kids into the car for their annual awkward summer at her parents' palatial Hamptons estate, and by the time they're on the Long Island Expressway, you have a good sense of how they work as a couple and what issues they're dealing with with all four kids. (There's a strange moment involving their older son that's perhaps one dramatic incident too many in the early going, but I also understand why Treem might want to liven up a sequence that's otherwise about familiar family drudgery.)  And a brief glimpse of a dinner with Cole's mother and siblings is all we need to understand the very different life he and Alison have lived from people like Noah that come out to the Hamptons just for vacation.

I've always found infidelity as a subject much less interesting than Hollywood has. When I heard about this show, I was cold to it, even with these actors involved, even with Treem running things. But the first episode, at least, is terrific, with a distinct, involving tone, and it does very right by its leads.

I'll check back in after I've seen some more episodes, but this is a fine start to what promises to be a very messy story.

Alan Sepinwall may be reached at sepinwall@hitfix.com


NOTE: I'll have a post up Sunday night after the first episode finishes airing on Showtime. Many of you may have watched it already On Demand or online, but please keep major plot details vague until Sunday.

Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at sepinwall@hitfix.com