In the hilarious French film A Good Doctor, an unwell emergency doctor recruits a totally unqualified courier to perform his rounds.
There's an old theatrical quote from the deathbed of a famous actor: "Dying is easy...", he's meant to have said, "..comedy is hard".
And after all too many films that backed that up, I found myself popping into another French Film Festival title, expecting another harmless bit of Gallic fun.
The English title was A Good Doctor - though in France it's simply called Docteur?
It was certainly fun, but it was rather better than that. It was one of the most expertly put together pieces of work I've seen for donkey's years, though looking back I shouldn't have been surprised. Just look at all the elements: comedy or farce, a doctor, a courier, a substitute - all French words!
A Good Doctor opens on the aging, disgruntled emergency doctor Serge. He's the only on-call doctor on the night before Christmas. He hates Christmas anyway - and he takes it out on another all-night worker Malek, a bicycle courier delivering meals to partygoers.
Malek is as cheerful as Serge is Scroogelike. Until disaster strikes.
Serge accidentally runs into Malek's bicycle. This is bad for both of them. Malek can't deliver anything without transport, and Serge has thrown his back out.
He can barely move, let alone climb the many stairs to his various patients. He tries to call in sick, but there are no available replacement doctors. So there's only one thing for it.
Serge offers to give Malek the use of his car. In exchange, he does the legwork for Serge's house calls. It'll be easy, he assures Malek. Stay on the line, I'll walk you through the medical stuff by phone.
What, as they say, could possibly go wrong?
What goes right is an old-fashioned, brilliantly constructed French farce - the sort of thing that old masters like Moliere, Feydeau and Jacques Tati have been doing for years.
It all starts with the writing. A Good Doctor is as tight and mathematically contrived as most American examples are approximate, and dependent on inspired ad-libs.
Initially, Malek is very tentative - understandably - particularly when confronted with his first patient, a large gentleman requiring rather more hands-on treatment than he was expecting.
And some of his other patients are puzzled that he seems to keep conferring with his inside pocket.
But under the instructions of his medical puppet-master, so to speak, Malek becomes more confident.
At least confident in his bedside manner. He continues to find it difficult remembering his name - Dr Serge Mamou-Mani. Or precisely how to work the digital thermometer.
The secret of a French farce is in the characters. Everything happens for a reason, and everyone has their reasons for doing it.
We discover why Serge hates Christmas so much, and why he's so short with his daughter-in- law Rose. We find out why Malek was on a bike in the first place, and how his plans for the future change that night.
Things go wrong, things go right and the performances by expert farceurs like Michel Blanc as the real doctor and Hakim Jemili as the fake one are perfectly judged, light as a feather and supremely human.
It's funnier because nobody plays it as a comedy. It's played absolutely straight, and the proof of the pudding was in the laughter.
A Good Doctor was laugh out loud funny all the way through, and the only concern was that such a perfect setup might stumble before the end.
Not at all. We were in the safest of hands - a first-time writer-director called Tristan Séguéla.
I'd never heard of him either, but on the strength of A Good Doctor, I look forward to his next film. Yes, comedy is hard, but when you get it right, it's…. well, there isn't an English phrase for 'joie de vivre', is there?
