[Warning: spoilers contained herein] Ben Stiller‘s The Secret Life of Walter Mitty (20th Century Fox, 12.25) is a smooth and supple dreamscape romance about a timid, do-little Manhattan daydreamer (Stiller in the title role) who suddenly morphs into a fearless adventurer at the drop of a hat, and in so doing gets the girl (Kirsten Wiig) at the end. To me it’s an odd duck fable — smart but soft, manipulative but emotionally plain-spoken for the most part — that’s aimed at the none-too-brights who went for Forrest Gump and/or The Curious Case of Benjamin Button. In my book it tries too hard to soothe and mollify to rate as an Oscar contender. That’s not a putdown, just a qualifier. The fact that Mitty is playing the New York Film Festival almost three months before its Xmas day opening suggests that Fox and Stiller are expecting award-season traction. Well, at least it’ll make money. Watching it is like sitting in a warm bath. It’s comforting. Every frame says “steady as she goes.”

Mitty is a first-rate thing in terms of Stiller and Wiig’s performances and in several below-the-line ways. (The subtle CG is excellent and often elegant.) But the second half is really quite silly or at least willfully bizarre, and I’m sorry for that. As a longtime Stiller fan I was really hoping to be stirred or even mesmerized. Nope.

It’s a bit strange that Stiller, an obviously smart and shrewd guy and hardly inclined to deliver sentimental mush as a director, would make a film like this. It’s actually half-decent if you put away your beefs and just let it seep into you, but it’s weird that Stiller would capitulate this much to what seems to me like a big-studio mindset. Because Mitty is, after a fashion, basically a smart, reality-based transformation film. Under the skin it’s a semi-grounded Spider-Man. But that’s the mainstream movie business these days. The suits wanted a movie about a middle-aged mouse who suddenly becomes a doer and a go-getter, and Stiller has given them this. It’s just that there’s no way to believe it, and I’m saying this as someone who really wanted to going in.

The 42 year-old Mitty, of course, is based on the withdrawn, middle-aged daydreamer created by James Thurber in his 1939 New Yorker short story. The film’s version works as a negative archive manager for Life magazine, which in actuality shuttered 13 and a half years ago as a regular publication. (This plus the Thurber origins make Mitty a kind of time-trip thing.) And yet in Stiller’s film Life is only just being changed into an online-only deal, and for the hiss factor there are three beardos (including chief asshole Adam Scott) in charge of the workforce transition. We all know about guys in expensive suits who evaluate job performances and fire people — been there, done that, stock villains.

The first half is about Stiller being covertly smitten with fellow Life employee Cheryl (Wiig) while trying to find a missing negative that was sent to him by the magazine’s big-dick photographer, Sean O’Connell (Sean Penn), who travels around like a ghost and is anything but easy to get hold of. Mitty spends part of his time trying to find the O’Connell negative and part of it hanging with Cheryl (at one point he attempts to bond with her young son by showing him how to do skateboard tricks). But more generally he spends lots of time fantasy-tripping about cool things he’d prefer to be doing. Mitty imagining himself as a studly superhero or savior or Hulk of some kind. Anyway — so far, so good.

Except the fantasy vs. reality stuff begins to blur. When the skateboard-demo scene happened I was going “wait…the dweeby, mild-mannered Mitty knows how to perform the kind of skateboard stunts that only X-treme sports champions can handle for the most part?” And then Mitty, desperate to find that missing negative, suddenly decides he has to fly to Greenland (and then Iceland and then some Middle-Eastern country) to find O’Connell, and it’s here when the film loses its mind by depicting his adventures in these territories as vaguely fantasy-like…and yet they’re real-world. Mitty is suddenly a real-world guy who eats boldflakes for breakfast — not just a “doer” but a fearless adventurer and life-gulper, a guy whom Robert Capa or Tim Hetherington would greatly admire.

I didn’t know what to think when this began to happen, but I was waiting for the other shoe to drop. And it didn’t. Mitty is really jumping out of a helicopter into the North Sea and really trading a rubber superhero doll for a kid’s skateboard (a deal that no real-life skateboarder would ever accept) and really making his way across half of Greenland (or is it Iceland?) on that skateboard and really tracking down O’Connell across Tibetan glaciers. How is it that a guy whose primary activity is saying “if only” to himself is suddenly a subject for Outside magazine or…you know, some kind of 21st Century Ernest Hemingway or Sean Flynn or whomever? We’re talking “suddenly” in the sense that Ebenezer Scrooge became a warm and loving man after being visited by the ghosts of Christmas past, present and future. An abrupt character change that comes out of fucking nowhere.

But there’s a reason. The reason that Mitty suddenly becomes Amos Bouldcox is — ready? — because Steven Conrad‘s script wills it so. (Remember that Conrad wrote Will Smith‘s The Pursuit of Happyness and Gore Verbinski‘s The Weatherman — both fanciful duds pushing romantic views of life.)

In short, The Secret Life of Walter Mitty is so caught up in daydreaming that it daydreams itself into a kind of narrative cul de sac.

42 year-old guys are not caterpillars waiting to become butterflies. They generally don’t flip over like a pancake and become brand-new people. It’s wonderful when a somewhat older guy summons the character to make a big change and find new success, but it’s awfully rare. It’s hard enough to free yourself from loser habits in your early 20s. It’s five or ten times harder to pull yourself out of a hole when you’re 30. And it’s damn near impossible to change your life at 40-plus. There used to be an old saying that went “whatever you are at 30 you’re going to be a lot more of.” I was a late bloomer myself. My life didn’t really kick into gear until the mid ’80s or thereabouts. And I didn’t find my true groove until the late ’90s when I started this column. But I’ve known a lot of mild-mannered Gus types and I know how their lives tend to evolve for the most part. They don’t become Tyler Durden.