This is so clever it's almost surreal. The driver following us thinks so, anyway. The sun is hiding and we're about to join an autoroute, so the hood of our Audi S5 Cabriolet needs to be closed. The busy traffic out of Monaco is moving happily at the 50km/h urban limit – 31mph – but, even so, I press the "close" button.
Gentle whirrs and clicks emanate aft, the hood emerges from behind the back seats and in a motion reminiscent of a swordsman's thrust, it slices forward as it unfolds. That's why you can do this while driving at normal traffic speeds; the hood contrives not to act as a vertical sail at any point in its contortionist routine.
Seventeen seconds after I first pressed the button, the hood is shut, windows are up and we are snug. Now we're on the autoroute, aiming for the mountain roads that will let us discover if the convertible Audi – from a cool £42,000 – is any more than a seafront cruiser for beautiful people (the latter qualification being one I fail, with honours). And the silence is astounding. There is no detectable rush of wind, and I can hardly hear the exhaust note at a gentle 80mph canter. It is like being in an S5 coupé, complete with plush headlining. I have never known a better hood.
Earlier, we drove a humbler version of the open Audi, an A5 with a 3.0-litre turbodiesel engine. The hood is the same, the engine less powerful than the S5's (of which more in a minute). Both have seven-speed, double-clutch transmissions, both have Quattro four-wheel drive as standard, which nowadays diverts more energy to the rear wheels than to the front unless grip conditions dictate otherwise.
But instead of the S5's racy, body-gripping front seats, the A5 has more conventional chairs, with optional warm-air vent at neck level. It's the same idea as Mercedes-Benz's "Air Scarf", but as yet has no Audi name. "Virtual Pashmina" would fit the bill, I thought, and my invoice is on its way to Audi.
These mainstream A5 Cabriolets come with the same engine range as the A5 coupé, so you can have – initially – 2.0 or 3.2-litre petrol units or that 3.0-litre V6 turbodiesel, with 2.0 and 2.7-litre turbodiesels to follow. These last two are front-wheel drive only; the others have a Quattro option except where it's standard.
So the experience is much as it is in the coupé apart from the slightly softer responses that go with greater weight and the more flexible structure caused by the lack of a rigid roof. And, of course, the potential for wind in the hair, something felt with the greatest force by brave souls in the back seats. But if just two of you are travelling, you can fit a wind deflector across the rear-seat space.
That driving experience encompasses a smooth ride with hardly any body shudder, quiet engines, a feeling of unshakeable quality and secure cornering. But it's relaxing rather than exciting. Then you try the S5, and discover why we needed those mountain roads.
An S5 coupé has a 4.2-litre V8 engine with 354bhp and a bit of a CO2 habit (288g/km). The S5 convertible does it differently, with the 333bhp, supercharged, 3.0-litre V6 found in the excellent S4 saloon and estate car. It's a great engine whose carbon contribution just snicks under the gas-guzzler threshold with a 224g/km CO2 score.
And with the roof lowered again – 15 seconds for the opening – I can hear the engine's mellifluously potent tunes all the better. The gearbox's automatic mode works very well, but such is the engine's crisp, eager nature that it's a crime not to use the paddle-shifts. Then you can hear the happy howl of high crankshaft speeds as they reflect from the rockfaces, not too loud, but thrillingly, uncannily, like those of a Porsche 911, and savour the muted pops and burbles issued with each gearshift.
Twisting roads become a joy, the (optional) Quattro Sport differential speeding up the outside rear wheel relative to the inside one to help point the S5 into a bend. Can this be related to that S5 coupé that so disappointed me at its launch, which did its best to disguise the new transmission and suspension systems intended to rid Audis of their former lugubrious, nose-heavy feel? Well, they certainly work now.
The S5 has a split personality, at once glamorous convertible and soul-stirring sports car. Any open A5 is a pleasing thing, with a boot far more capacious than in a rival, hard-roofed coupé-cabriolet. But the S5 is on another level. Open four-seaters come no more satisfying than this.