As advertised, “The Good Liar” keeps its promise. Helen Mirren and Ian McKellen share the screen for the first time, and it’s a wonderful thing to behold. The two have never been more revealing. As McKellen’s Roy Courtney and Mirren’s Betty McLeish sip cocktails on their first date, the two actors slip into their roles as out-of-touch old-timers. “Have you ever met people on the computer device before?” Betty asks awkwardly. Roy pauses, looks around the room, and replies, “Yes.” He too is playing the role of a clumsy old fellow. But Roy is actually a confidence man after the widow’s estate. After the date, he complains to his buddies that her house was “like being covered in beige.” Audiences will have a similar problem with this film because while the two leads are delightful, they’re just not enough and the film ultimately ends up like being draped in monotone. It’s a mystery that is mysteriously boring.

Spinning a successful yarn is itself a lie. Misleading an audience through a maze of fictive twists and turns, only to reveal that the past two hours—or 500 pages— was a trick is not an easy thing to pull off. It’s a trick Nicholas Searles‘ novel (of the same name) managed in 2015, and it’s a sleight of hand maneuver that director Bill Condon can’t recreate. Early on, as the chemistry sparks, things move at a youthful pace. The two go on a date to “Inglourious Basterds,” take walks around London, and discuss all the things that are great about the digital age. They can’t stay hip for long, though. Betty throws out her hip and Roy fakes a leg injury, giving him the opportunity to move in, with the hopes of pouncing like a cat on a limp mouse.

Just one problem: Betty has a grandson (Russell Tovey). More specifically, Betty has a grandson who sees through Roy’s bourgeois charm. Isn’t it precarious to joint bank accounts weeks into a relationship? He reasons as much when Roy’s banker (Jim Carter) shows up for champagne. It will take”Downton Abbey” fans a few minutes to accept Carter as a bad guy, instead of the lovable Mr. Carson. But it’s fascinating, then beguiling, to see these talented performers play against type.

What’s less interesting is the world they live in. Instead of discerning Roy’s mind games through ambiguous atmospherics or a brooding tone (like le Carre), ‘Good Liar’ takes a commercial approach to suspense, but it’s one that should’ve been darker. London might be known for its gloomy weather, but that doesn’t mean the grayness had to extend to everything and everyone. And if you’re going to insist on poor weather, you might as well have it mirror the convoluted minds of the protagonists (like in “Don’t Look Now“). Instead, Condon, who is unable to portray the feelings of his subjects in cinematic terms, settles for mirroring the atmosphere to the color of his character’s hair.

That isn’t to say there aren’t bright moments. Every moment Mirren and McKellen share the screen is a moment worth watching. When the two sit down for dinner, you can see the wheels turning in Roy and Betty’s heads, their eyes investigating each other’s mannerisms like poker players. Cars start passing by the house. On holiday in Berlin, Roy disappears as he dodges a tail in a subway. Jeffery Hatcher’s script, along with John Stevenson’s mise-en-scene, keeps the trail of clues coming. That trail leads to some questions. Who’s conning who? Why is there so much red in the background all of a sudden? What the hell is this ending?

The final twist gives new meaning to “gilding the lily.” Condon’s third act throws the past hour out the window to make way for a preposterously pretentious World War II allegory, one that makes no sense in retrospect. That twist needn’t be spoiled here. Just know that the ending is a bizarre paradox: it’s the only part of the storytelling that isn’t bland, yet it’s the worst part of the movie. Mirren and McKellen are superb even in these dire circumstances. But to call anything else “superb” in this flavorless thriller would be a huge and dishonest falsehood. [C-]