LEE CHILD, author of the novels featuring hulking avenger/investigator Jack Reacher, has defended the selection of tiny Tom Cruise to play the series' towering, bulky hero, on the grounds that in Hollywood, there simply are no Jack Reachers. Everybody is small. It's like the Shire. Except the hobbits all live in 5,000-square-foot houses and drive SUVs.

Cruise, obviously, is not a match for the character's exterior. The question is whether he can convey the character's interior. You have to buy Cruise as a tarnished idealist, a man whose ugly, theater-of-war experiences (as a military detective) have left him with a diminished belief in his country.

Diminished, but not extinguished. Reacher is in many ways an update of Phillip Marlowe - the freelancing knight errant whose cynicism is the armor that guards the heart of a believer.

This is where Cruise seems a little out of his depth - on screen, his Reacher is a conventional, easily readable action hero, centerpiece in what turns out to be a brisk, competent thriller.

And in troubling ways, a standard one. It's worth noting that absent the recent tragedy in Newtown, Conn., we wouldn't give a second thought to the movie's opening scene - a gunman with a rifle picking people off in a park, including a mother running in terror while holding a child in her arms. It's strange to step back and realize how we accept this as cultural wallpaper.

The shooter is arrested, a terse detective (Daniel Oyelowo) accumulates the evidence for an open-and-shut case and hands it to a defense attorney (Rosamund Pike) who takes it apparently to anger her father, the prosecutor (Richard Jenkins).

It's all airtight, except the shooter, a former army sniper, makes a cryptic request that his attorney contact Reacher, the retired investigator, a shadowy figure of mysterious and unknowable motives, proud to be "off the grid," in every sense of the word.

Director Christopher McQuarrie (he wrote "The Usual Suspects") gets Child's style of storytelling just right - smart and abrupt, like Reacher himself. Reacher appears and starts tearing the case apart with his singular mixture of ruthless brawn and Sherlock Holmes-like powers of deduction. McQuarrie's movie follows the sharp, violent contours of the story with aplomb.

It holds up fairly well until the climax, which, alas, looks like something out of an old "Mannix" episode - if Werner Herzog were to guest star on "Mannix." Yes, that's Herzog, appearing as a Euro-sadist bad guy. His signature move - he gives blundering henchmen the choice to either chew off their fingers or take a bullet to the head.

From the evidence presented, it is better to give than receive the knuckle sandwich.