Five teams have been set the challenge to race across the breadth of Canada, passing through seven checkpoints, taking them from the Pacific coastline to the edge of the Arctic and the shores of the Great Lakes, ending up at their final destination on the Atlantic Ocean, St. John's on the island of Newfoundland, the most easterly town in North America. A £20,000 cash prize is at stake.The remaining pairs must now navigate to the fourth checkpoint, the remote outpost of Churchill, where polar bears can outnumber people. On Hudson Bay, at the edge of the Arctic, Churchill is not connected to the rest of Canada by road but by a twice-weekly train, and the teams have just three days to catch it. It's a journey that will take them from Alberta's major cities of Calgary and Edmonton, before the Rockies make way for Saskatchewan's great prairies and badlands.As the train makes its way from Winnipeg to Churchill, the teams need to work out where they can catch it. With the clock ticking, every decision counts for the racers, as they work together once again to reach that all-important checkpoint to be one step closer to the finish line and the £20,000 cash prize.