Will Mellor and Kirsten O'Brien take on the ultimate driving challenge, travelling the globe learning to drive and race the world's biggest, most expensive and hardest-to-master vehicles in a bid to find out who is the better driver.

With Will trailing Kirsten 2-1 at the series half-way point, the competition gets personal and the rivalry intensifies as they head to Canada to drive the world's most sophisticated amphibious vehicle, the 47-tonne, two-million-pound go-anywhere Arktos.

Brimming with confidence after her win driving the 100-tonne Terex truck in Scotland, Kirsten is about to face a fierce fightback as Will battles to break even.

Over three intense training days, mentor Bruce Seligman puts Will and Kirsten through a series of lessons and tests to prepare them for a final race, where there can only be one winner. The Arktos is unlike anything Will and Kirsten have ever driven before and as they grapple at the controls on land, river and even the Pacific Ocean, the unthinkable happens and Kirsten crashes the supervehicle. Distraught and emotional, she has to take stock.

Can Kirsten restore her confidence and widen the lead, or is Will about to take victory and level the score? Show less