The dream team of Helen Mirren and Ian McKellen assemble for a mature thriller directed by Bill Condon (Gods and Monsters, Beauty and the Beast) and based on the novel by Nicholas Searle. McKellen plays Roy, a scheming con man who targets wealthy widows and fleeces them of their cash with elaborate schemes. His latest mark is Betty (Mirren), whom he meets online. The pair become closer, with Roy even plotting to move into Betty's house, but her son Steven (Russell Tovey) is suspicious of his mother's new companion – as well he might be.

It's tricky to discuss without spoilers: suffice to say, it ends up as a blend of several different genres which don't necessarily fuse well on screen. The most enjoyable aspect is the con artist comedy: Roy pretends to be a respectable elderly gentleman to Betty, but one quick outfit change later and he's ripping off Russian investors in the back room of a strip club. McKellen pulls this contrast off with relish, quickly switching from the benign hangdog expression he wears for Betty to the knowing grin of a smooth entrepreneur.

The film's plot mechanics provide more of a challenge to Mirren and Tovey, and, while they ultimately fare well, their performances are inherently less enjoyable. As for other supporting cast members, Downton Abbey's Jim Carter puts in a pleasing turn as Roy's slightly more circumspect partner in crime, and Mark Lewis Jones does good work as a hapless victim.

As the plot thickens, the flashbacks increase, and some viewers might find the change of tone a bit of a jolt, whereas fans of the book will know the score. It all adds up to a film that's flawed, diverting but far from essential, unless seeing Mirren and McKellen together is on your bucket list. Perhaps next time they'll join forces for something more memorable.

General release from Fri 8 Nov.