Although it won't officially debut until the 2013 Frankfurt Auto Show, Porsche is busy testing prototypes of its upcoming 918 Spyder. Our always-reliable spy photographers have just managed to snap pictures of a 918 test mule doing some hot laps around the Nurburgring, and it looks delicious in greyscale Martini livery. Unlike the German sportscar builder's previous supercar, the Carrera GT, the 918 Spyder will be a plug-in hybrid.

Power will come courtesy of a 4.6-liter V8 good for 570 horsepower as well as two electric motors for a combined output of nearly 800hp. Styling-wise, we can see that it pays tribute to the 917 racing cars that took part and won Le Mans back in 1970 and '71, but in a more modern form that looks something like a new Cayman that's been juicing. And we mean that in the best possible way. The 918 is built around a full carbon -reinforced plastic monocoque, augmented by adaptive aerodynamicsand steering. Production will, of course, be highly limited, and you can expect to see pricing at around $850,000.