The speculative doodlings of the Roadster-transformed-to-take- a-fixed-top had been gathering dust at BMW's Munich design studios since the late 1990s when they were rediscovered last year.
They were so good that what started out as an "unofficial" side project to the now familiar Z4 Roadster was given the green light and will be on sale next month.
To give it a proper airing - the car that is, not the sock - the German manufacturer allowed me to drive it around the wilds of Scotland.
And despite its advanced "design" years, the coupe still looks as fresh as a daisy.
BMW describe it as a pocket GT and that's a fair description. It works best in bright colours - my favourite being bright red - while it's a little lost in black.
It's best viewed side-on, a perspective which provides a clear view of its neat, dome-topped roof. And it has kerb appeal in spades.
There are three versions to choose from, all of which have the updated rear end recently provided to the Roadster.
The Z4 3.0si SE Coupe comes with 265bhp, a 0 to 62mph time of 5.7 seconds and a price tag of £31,400.
Better toys
An extra £1,525 buys a similar car with a Sport badge and slightly better toys.
At the top of the range is the 343bhp M Coupe, a car which is 0.7 of a second quicker to 62 and almost £10,000 more expensive, at £41,285 on the road.
The cognoscenti will identify it from the tantalising M badge and a set of four tailpipes.
And so, salivating like Pavlov's dog at a bell ringing convention, I climb into the M.
I like the dials in front of the driver but feel that the rest of the dash looks a bit Bang and Olufsen circa 1984. Other than that, there's really only a big fat steering wheel with an M badge (there's no M button) to tell that you're in the sportier version.
Insert the key, switch her on, and you're rewarded with a precise mechanical roar rather than an aggressive exhaust rumble.
The seat is supportive and bucket-like yet equipped with lots of buttons to ensure it moulds perfectly to your back and bottom.
And soon we're off and climbing steadily through the standard six speed box. But at the risk of sound metrosexual in a country where the men are hard enough to wear kilts, I'd say it feels a little bit too extreme.
The clutch is snatchy and unforgiving, the brakes incredibly sharp and the additional pace only to be appreciated by really enthusiastic and confident drivers.
Worst of all, it's let down by flyweight steering which feels fine at low speeds but leaves you with the fear of bouncing off the side of the road when travelling at high speed in a straight line.
Confident
Even so, with its wide body and fat wheels, the Coupe feels confident into the corners.
But I'd say that driving this close to the edge of your seat could soon lose its appeal. And so, tail between its legs, Pavlov's pooch tries the 3.0litre version for size.
The nerves are soothed at the first dip of the clutch. It feels much easier to get on the move and the knuckles wrapped around the skinnier steering wheel aren't anywhere near so white.
It feels far easier to enjoy myself, taking advantage of the power whenever I feel like it but comfortable enough to ease off and enjoy the view.
It still suffers from the same overly light steering as the M but will be much easier to live with.
This car has still competition from the likes of Porsche and doesn't quite have the substantial yet sporty feel of its rival.
But it's still a rewarding ride and carries the additional cachet of being the new fixed lid on the block.
You get two seats and 340litres of boot space and the promise of near exclusivity on the roads, with only 1,000 Z4 Coupes set for sale in 2006. Two hundred will be the friskier M variant. You can also opt for an automatic gearbox.
But waiting lists - and order times - are expected to be long.
The good news if you want one is that the car without the M badge is cheaper, better and four times easier to lay your hands on.
Keep the £10,000 you save somewhere you might find it next time you have a clear out {hellip} that's got to be better than finding an old sock.
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