A man edges along the 21st-story ledge of a midtown New York City hotel. He's an ex-cop and a convicted thief on the lam, straight out of Sing Sing, and he's threatening suicide.

Sam Worthington, of "Avatar" and "Clash of the Titans," plays this character, Nick Cassidy, and it is odd to see Worthington on a precipice without winged beasts or blue friendlies buzzing about his head. The only thing buzzing in "Man on a Ledge" are little gnats of narrative improbability.

Like the more antic "Tower Heist" a few months back, "Man on a Ledge" exploits populist rage against corrupt bazillionaires as it spins a tale of a high-risk revenge burglary in Manhattan.

Unlike "Tower Heist," though, "Man on a Ledge" confines its protagonist to a thin sliver of concrete for much of its 102 minutes. While Nick is up to ... something out there, on the ledge, a police negotiator played by Elizabeth Banks argues with another cop (Edward Burns) about how to talk him down.

Banks is a skillful actress, particularly in comedy, but she doesn't easily suggest "hard-bitten."

You can say this for screenwriter Pablo Fenjves' story: It stays busy. It starts in the hotel, moves to the ledge, then swoops back into a one-month-earlier flashback, explaining how Nick got there, why he went to prison in the first place and how he managed to turn a furlough for his father's funeral into an opportunity for escape.

Nick asserts his innocence regarding the theft of the $40 million Monarch diamond, the one owned by a monster capitalist played, or rather sniveled, by Ed Harris.

So many details eat away at our engagement with this picture. Why wouldn't the negotiator notice Nick has an earpiece and a habit of murmuring aloud? Why does the distance between the ledge and the pavement seem to vary from shot to shot, depending on whether we're watching actor-harnessed action filmed on location or actors doing their thing on a mock-up of the location?

Jamie Bell plays Nick's younger brother, in cahoots with his fiance, Genesis Rodriguez. Anthony Mackie, a terrific actor, brings some artful ambiguity to the role of Nick's colleague from his police force days.