"Do I make you nervous?" asks renegade CIA agent Tobin Frost, eyeballing the equally treacherous British operative sitting beside him in Cape Town, South Africa, traffic. "Always," replies the Brit, as a sniper's bullet ventilates his skull. Clearly there's something dangerous about hanging out with Tobin Frost.

The same can be said of Denzel Washington, who brings his cobra smile and a surfeit of charisma to Swedish director Daniel Espinosa's often frenetic action thriller "Safe House." Co-starring the ubiquitous Ryan Reynolds, the film works well, or not, according to who is on screen: As Tobin's outmatched opponent, CIA "housekeeper" Matt Weston (he maintains the agency's safe house in Cape Town), Mr. Reynolds brings an appropriate degree of naiveté and boyishness to a film that's largely about loss of innocence. But whether he's right for the role, or not, is irrelevant: What we want to watch is Mr. Washington, and of him there is not nearly enough.

It's curious, given Mr. Espinosa's often furious style and indulgence in artistic mayhem, how much of "Safe House" neatly fits into predetermined slots. As Hollywood's go-to callow youth, Mr. Reynolds is a casting director's no-brainer: Matt is angling for a post in Paris, where he would be much nearer his girlfriend (Nora Arnezeder) and could get his stalled career in gear. Ideology? Absent. Similarly by the book is the casting of his three superiors: Sam Shepard shows up these days whenever anyone needs a gray eminence; Brendan Gleeson is a slippery character, something a spy movie certainly needs; and Vera Farmiga is filmdom's ripe actress of the moment, with the looks, intelligence and just enough years to make her plausible as a high-ranking CIA officer.

The wild card is Mr. Washington. Even though he's too attractive and engaging to be a natural villain, you can't say he doesn't try: He won an Oscar for playing the bad guy in "Training Day." He was charmingly sinister in "American Gangster." He even went out of his way to be unlikable in "Unstoppable."

In "Safe House," he's a near-mythical rogue agent who has sold out the CIA time and again to the highest bidder. Spoken about in hushed tones, he seems to be Langley's version of Voldemort, although when he appears in Cape Town, clad in a wide-brimmed hat and sweeping black coat—a cloak-and-dagger affectation that's both marvelous and marvelously overdone—his intentions are unclear. He is shown injecting something into his side, which later turns out to be a tiny capsule containing information valuable enough that every mercenary and Mossad agent in town is after him. The heat becomes so intense that Tobin turns himself in to the U.S. embassy. Better that than sure death on the street. Perhaps he'll be handed over to someone inept enough to let him get away?

Enter Matt, who can't understand why he hasn't been given bigger things to do. (It's clear enough to us.) A band of CIA agents arrives at the safe house, and immediately subjects Tobin to water torture. "Is this legal?" Matt asks worriedly—a line which, in terms of character development and economy, is near perfect, absolving him from adult responsibility and affirming the agency's good judgment. When the CIA officers are swiftly blown away by an invading army of opposing agents, Matt is left holding the bag, i.e. Tobin, and we brace ourselves for a mismatch.

The fact is, we're already in one. "Safe House" is a sturdy enough thriller, but one that consistently defaults to the less interesting of its two lead characters. The ads for the movie imply that Tobin is some kind of Hannibal Lecter, and Matt his Clarisse, but there's only a hint of that. Much more time is devoted to Matt keeping Tobin in check, or chasing after him once he flees, taking Mr. Espinosa's better instincts with him: The psychological nuance of "Safe House," which seemed so promising, gets subsumed by action, which is ambitious but less bracing than what Mr. Washington seemed to be cooking up behind that smile.