Sir Ian McKellen is 80 years old and Dame Helen Mirren is 74. Individually, these veteran thespians, each with decades of work on stage and screen under the belts, are capable of out-acting, outrunning and outgunning performers one third their age. This is not disputable. They can both go big, broad, and Full Metal Bard when needed, or be very subtle and nuanced. Whether these two are in big-budget blockbusters or quaint period-piece dramas, they are respectively dynamic as hell. Put them together, and theoretically it’s like pairing the immovable force with the irresistible object. You’d watch McKellen and Mirren do just about anything together, much less an adaptation of a well-respected novel about a con man slowly circling his lonely hearts mark. It appears to be the ideal vehicle for both of them. And what’s that old saying about appearances being deceiving? That particular maxim is something akin to The Good Liar’s mantra, so maybe it makes a warped kind of sense that what seems like a sure thing upfront ends up being a sham. It introduces both of its main characters as unreliable from the jump: We see McKellen’s dapper elderly gent and Mirren’s elegant widow filling out online dating profiles, him dragging on a cigarette as he checks “No” in the smoking box and her sipping wine as she claims not to be a drinker. They meet for dinner, and after a few pleasantries, confess that neither of them have used their real names. He’s Roy Courtnay, a slow-moving man of modest means who’s estranged from his son; she’s Betty McLeish, a former college professor living in the ‘burbs just outside of London and sitting on a lovely little nest egg. What isn’t revealed, naturally, is that Roy is a con man. He specializes in complex financials scams he sets up with his partner Vincent (Downton Abbey’s Jim Carter). But he’s not above, say, charming an older woman and then liberating her of her life savings. Soon, Roy has worked his way into Betty’s heart, and then right into her home. Her grandson Steven thinks there’s something dodgy about this geezer with the gammy leg – the limp, like so much with Roy, is fake – worming his way into his gram’s life. But Betty has grown fond of this man. She may gently rebuff his advances, yet you can see how his presence and amiable demeanour warms her up. Betty doesn’t even mind that her new companion’s “financial advisor” keeps popping around, advising her to combine all of their assets together into one banking account. Roy is setting a trap. Or perhaps, unbeknownst to him, he’s walking into one.Protocol suggests that this is the part where anyone describing further details of The Good Liar, especially to those who have not read Nicholas Searle’s 2016 novel of the same name, should begin to tread lightly. Anyone who’s had the twists and turns of a con-man movie ruined by some mouthy jackanapes knows that a good deal of the fun is discovering this for yourself. By the same token, viewers familiar with these particular kinds of A-list affairs can assume that nothing should be taken at face value. It’s probably safe to point out that Roy has a scar on his neck that he seems reluctant to say too much about. And to mention that Steven is a historian who’s studying WWII and, in particular, the complicity of architect Albert Speer. And to note what might seem like a casual vacation may have a secondary agenda attached to it. You’re waiting to see what the endgame is here – and when director Bill Condon (Gods and Monsters, Chicago, the live-action Beauty and the Beast) and screenwriter Jeffrey Hatcher (The Duchess, Mr. Holmes) finally do lay it all out, you may find yourself picking your jaw off the floor. Not in a good way, either, since so much of the denouement feels like it’s simply dropped out of the sky and landed on your head. The filmmakers have been careful not to give away too many hints along the way. But you never really feel like they’ve set the story up to feel like the numerous climaxes and codas – there are several, all piled on top of each other – make sense with what’s come before them. The goal, you assume, is making people sense that a missing piece has finally been slotted into a puzzle, but the result is closer to reading aloud a Narrative 101 Mad Libs exercise. One assumes that the book makes such quick-left-turn moments seem logical. Here, sharing time with a subplot involving a Roy-engineered scam and some WTF red herrings, the entire last act just translates as ludicrous to the extreme.The real question is: Are you willing to endure all of that random swerving for the simple pleasure of these performers’ company? Both actors are, unsurprisingly, bending over backwards here to sell these characters and establish enough screen chemistry to smooth over a lot of rough patches. McKellen is incredibly adept at playing cunning and slippery; he’d be a perfect late-in-life Tom Ripley. (There’s also a sequence where you see Roy virtually deflate before your eyes, and that lets you observe how McKellen can turn a simple glance back into a three-act melodrama.) And Mirren, always a dependable presence, knows exactly when to underplay Betty’s naive attachment to this mysterious stranger and when to suggest that there’s a lot happening behind those eyes of hers. They play off each other beautifully despite the material, and they get a chance to indulge in the aforementioned range of sound and fury. Yes, you would watch these two in virtually anything. You just wish it wasn’t this. They deserve something sturdier and far less head-slappingly preposterous and that’s the truth.