A rare sighting of Nessy, the Loch Ness Monster, has put her in danger from a Monster Hunter's hi-tech boat. The Trekkers race to Scotland and have an underwater adventure in a special Trekker Submarine to try and find Nessy and protect her. Mip's fears of Monsters however taints his view of Nessy, until they discover she has a baby, and is actually just a kind animal, frightened of being captured. Mip bonds with the Baby Monster, and revises his view of what makes something a Monster. He ends up taking a heroic stand to protect Nessy and her baby from Monster Hunters once and for all.