As the little train starts the first part of its epic journey, it becomes clear exactly how difficult the challenge will be. The team's attempt to use the miniature train ferry that they've built doesn't go well, with the train drifting towards a wall of water... Meanwhile, the track teams are battling in rainy and midge-infested conditions to lay more track. And the build team have to work out how to span a 60-metre viaduct by Aberchalder Bridge. It could flood at any point, so they decide to build another viaduct, but the sheer length of it makes it very challenging. And the train is making slow progress, with much more rugged terrain still to come.