Fisker surprised many at last month’s Detroit Auto Show when it revealed its striking Karma luxury plug-in hybrid sedan was headed for production and a 2009 launch. Here was a small coachbuilder promising to deliver a plug-in hybrid vehicle at least one year before heavyweights like Toyota and GM could. Now it plans to add to its arsenal by launching a two-door, four-seat convertible model as well.

The information comes from Fisker founder Henrik Fisker, who spoke recently at a J.D. Power event. Fisker showed a photo of the car with the label ‘top secret’ marked across it, reports Automotive News. Fisker definitely has some ambitious plans. Not only does it want to become a fully fledged carmaker (its current lineup includes a range of re-skinned BMW and Mercedes models) but it plans to expand sales into Europe for the first time next year and there could be more markets to follow.

The new plug-in hybrid powertrain for the Karma was developed by another company, Quantum Technologies, and it features a small petrol engine turning a generator to top up the car’s lithium-ion battery pack, which in turn power an electric motor driving the wheels. However, Fisker claims the Karma can drive up to 50 miles on a single charge and reach a top speed of 125mph and sprint to 60mph in just six seconds.