Three years after resigning from office - the only U.S. president to do so - Richard M. Nixon agreed to sit for a long conversation with David Frost, an English TV chat-show host who'd entertained a few politicians as guests, but more often could be found lobbing softballs at singers, actors, comedians.

The 1977 interview, aired over four nights and watched by more than 45 million people, offered the former commander-in- chief the opportunity to shine up his tarnished image, to restore some legitimacy to a sullied reign. (It also provided him with a very big paycheck.) And it gave Frost the chance to go for ratings glory, and to try to extract from Nixon a confession, or at the very least, an acknowledgment of wrongdoing. Both men had an agenda. Both had something to prove.

Frost/Nixon, the adaptation of Peter Morgan's play - with Frank Langella and Michael Sheen reprising their respective roles as the president and the interviewer - offers an engaging reenactment of this historic tete-a-tete. There is tension, as the two sit for their gentlemanly smackdown, Nixon cagey and adept; Frost, at first, seemingly out of his league, ill-prepared, but rising to the occasion.

Directed by Ron Howard in an almost reflexive "opening up" of the stage play for the screen (lots of globe-hopping, lots of hangers-on), Frost/Nixon is a must-see for political junkies, history buffs, and folks still fascinated by the paranoia-fueled follies of the twitchy, sweaty, decidedly uncharismatic 37th president.

Langella doesn't exactly mimic the awkward jests and gesticulations of Tricky Dick. Instead, he gets the rhythms of Nixon's speech, the body language, and then digs deeper to find the vulnerable and self-destructive core of the man who presided over the Vietnam War, brought a level of civility to U.S. relations with the Soviet Union and China, and then saw everything collapse as the bungled Watergate break-in exploded into a full-scale disaster.

Sheen, who played Prime Minister Tony Blair in The Queen (also scripted by Morgan), is fine as Frost. The film takes pains to show Frost's ambitions, his risk-taking (he borrowed heavily to produce the syndicated TV interview), his penchant for pretty women (Rebecca Hall is Frost's girlfriend, looking happy just to hang around), and his belated realization that he was onto some possibly history-making revelations.

Still, there's a shallowness about Sheen's performance. The actor shows Frost to be smooth and smiling, worried and distracted, but doesn't really do much more. Perhaps, there wasn't much more to do - a function of Morgan's screenplay, and of the congenial gadabout playboy and now-knighted Frost himself?

Frost/Nixon is not the epic gladiatorial face-off, the ricocheting verbal shoot-out that writer Morgan and filmmaker Howard imagined. With all these tertiary characters huffing and puffing around the two principals - Sam Rockwell and Oliver Platt as Frost's researchers James Reston and Bob Zelnick, and Kevin Bacon as Nixon's loyal aide de camp, Jack Brennan - the pressure gets diffused, the drama diluted.

But as a historical marker, a canny remembrance of a moment when politics and pop culture collided, the film's worth investigating. And Langella - well, he's in a realm all his own, a Nixonian universe where the flaws of human nature glisten like broken glass.