As completely ludicrous as it is at times, and as absolutely preposterous as it is at other times, it's still hard to hate "Vertical Limit."

After all, how many other movies can boast that they made even the simple acts of breathing and drinking liquids seem like life-threatening events?

But those are just a couple of the accomplishments by this mountain-climbing action-thriller, which falters several times during its initial ascent but which also improves dramatically in the second half.

If anything, "Vertical Limit" resembles nothing so much as those old Irwin Allen disaster movies that placed action over characterizations or coherent plotting.

Thankfully, this one's not quite as bad as those films were, but again, sometime it's only hanging onto that slippery slope by its fingertips.

One thing's for sure, this is definitely is not a movie for those afraid of heights, which is quite apparent from the white-knuckle opening sequence on the side of a sheer cliff (a scene shot in Moab).

It's there that brother-and-sister rock climbers Peter and Annie Garrett (Chris O'Donnell and Robin Tunney) lost their father. And though the two siblings have stayed close in the years that followed, Annie still blames Peter for cutting their father's rope loose — in spite of the fact that it may have saved their lives.

But Peter may get a shot at redemption when Annie and members of a summit team (Bill Paxton and Nicholas Lea) become trapped in a crevice while trying to ascend K2, the world's second highest and possibly most dangerous peak.

Desperately in need of water and air, the three seem to be doomed, unless a rescue team can reach them in little more than a day. So Peter, who hasn't climbed for years, volunteers, though he's obviously going to need help.

Unexpected aid comes from Montgomery Wick (Scott Glenn), a legendary recluse who lives on the mountain and who seems to have his own reasons for making the dangerous ascent.

Just getting to that point in the story seems to take hours, though director Martin Campbell ("The Mask of Zorro") does his best to keep things moving through an avalanche of bad characterizations, dumb plotting and equally corny dialogue (from veteran screenwriters Robert King and Terry Hayes, who should know better).

However, unlike "The Perfect Storm," which also sported disparate halves, the second half here makes up for that with a series of breathtaking sequences that will have audience members gripping their theater seats . . . or their dates.

That's probably a good thing because the aloof O'Donnell doesn't make the most magnetic hero, though he's probably adequate for what's asked of him here.

The supporting cast fares a little better, though Tunney is stuck in the victim-waiting-to-be-rescued role, and, as scene-stealing as he is, Glenn's hair extensions look pretty silly.

"Vertical Limit" is rated PG-13 for mountain-climbing violence, as well as warfare (explosions), scattered strong profanity (including one use of the so-called "R-rated" curse word), some crude sexual jokes and references, intravenous use of prescription drugs and brief gore. Running time: 126 minutes.

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