GRIFTERS: Nicky (Will Smith) agrees to teach Jess (Margot Robbie) the tricks of his trade.FOCUS (MA)

Stars: Will Smith, Margot Robbie, Adrian Martinez

Directors: Glenn Ficarra, John Requa

Screening: general release

Rating: ★★★★

A ROMANTIC caper movie is a delicate invention. If it’s nourished with the right mix of wit, ingenuity and sexual chemistry, you remain on the side of the con artists, whatever the nature of their scam. If not, you couldn’t care less.

It’s a lesson well understood by Glenn Ficarra and John Requa, the writer-directors of Focus. They set exactly the right tone as well as tweaking the plot with enough twists to keep your brain engaged. And it looks good.

Co-starring with Will Smith is Australian actress Margot Robbie, consolidating the career boost she got from her role in The Wolf of Wall Street.

His is the hard part. He’s playing the all-knowing conman to her eager apprentice – a role which could really set the teeth on edge in the hands of the kind of star who lets his ego show. But Smith keeps down the condescension levels.

He also sweats sufficiently during the plot’s suspense points to indicate the presence of a fully functioning nervous system.

It’s not exclusively a star turn. Smith and Robbie are surrounded by a supporting cast equipped with their own stock of slick lines. Ficarra and Requa have worked with both Jim Carey and Steve Carell and they’ve assigned a prominent role to another funnyman, Adrian Martinez. He plays Smith’s tubby chief lieutenant and, as you might expect, he turns every conversation into a comedy routine – always a high-risk undertaking. Here he carries it off.

Smith’s character Nicky Spurgeon, a professional conman, is picked up one night by Jess Barrett (Robbie) in the rooftop bar of a ritzy Manhattan hotel. Inevitably, they go back to her room, where their supposedly romantic encounter is revealed to be a scam as she and an accomplice make a clumsy attempt to steal from him.

He’s intrigued enough to seek her out the next morning and give her an impromptu but convincing tutorial in picking pockets. He then agrees to hire her as an ‘‘intern’’ and teach her the art of the grifter in New Orleans, shown in a smoothly executed montage and with by a soundtrack that converts it all into choreography.

From New Orleans to Buenos Aires, the script goes on laying on plot reversals so that you’re never sure what’s real and what isn’t.

And this raises a new challenge. Bamboozle an audience too often and you can lose them altogether. Yet Ficarra and Requa have laid the groundwork well, giving you such a good time that you’re ready to overlook the implausibilities because you’re enjoying the company.

And that, in the end, is what a good caper movie is all about. If you’re thoroughly – and elegantly – conned, and entertained, you can forgive the perpetrators almost anything.