S15, E3: Jeremy Clarkson, Richard Hammond and James May test the Aston Martin Rapide, the Porsche Panamera Turbo and the Maserati Quattroporte as they attempt to find the world's greatest four-seat supercar. After an early morning start in the City of London, the boys embark on a road trip across the south of England, stop off for a race around a closed-off business park, and end up undertaking a rather special chauffeuring job. Meanwhile, Richard is on the test track in two very different muscle cars, the Chevrolet Camaro SS and Mercedes E63 AMG. And there's a double dose of celebrity as Harry Potter star Rupert Grint and F1 ace Rubens Barrichello take their turns as the Stars in a Reasonably Priced Car.