Keira Knightley, left, and James McAvoy during a scene from "Atonement."

Part highbrow British drawing-room drama, part gritty war film -- and all entertainment almost all the time -- "Atonement" is a masterful study of both the hurtful and redemptive effects of imagination.

It's being billed as a Keira Knightley vehicle, but while Knightley plays a central role, she's just one character among many whose lives are forever altered by events both local and, in the form of World War II, global.

Words -- on paper, in people's mouths, wherever -- are given an enormous amount of power in director Joe Wright's film, based on Ian McEwan's novel. One word in particular sets off a series of tragedies that will take a lifetime to work through, and even then can't be set completely right.

"Atonement" begins with 13-year-old Briony Tallis (Saoirse Ronan) completing a play to be performed that night for visiting cousins and friends. Enormously imaginative and more than a little squirrelly, Briony from her window spots a curious exchange between her sister Cecilia (Knightley) and Robbie Turner (James McAvoy), the educated son of the family housekeeper, involving a broken vase in front of a fountain.

Briony's imagination, already piqued, becomes even more so when Robbie gives her a letter to deliver to Cecilia -- the wrong letter, as it turns out. An especially earthy turn of phrase leads to Briony's assumption that Robbie is a sex maniac; it also leads Cecilia into his arms, an event witnessed by Briony.

Thus inflamed, Briony will later that night accuse Robbie of a horrible crime he did not commit, an accusation that shatters more than one life.

Robbie eventually finds his way into the British army; Cecilia works as a nurse. So, too, does Briony, now 18 (played by Romola Garai), evidently as a sort of penance for what she now knows was a mistake.

McAvoy captures well Robbie's trudging through what his life has become. Garai outshines Knightley, who in comparison has much less interesting things to do. Most powerful of all is Vanessa Redgrave as an elderly Briony, now a well-known author whose words carry so much weight, so much intensity, so much truth, that they lift "Atone- ment" into a different, unexpected place. It's a place well worth visiting, and one you won't easily leave behind.

Bill Goodykoontz / The Arizona Republic