Elspeth and Angus discover a path leading to a hidden cottage. They meet a part-time witch - she's also a bus conductor. She is trying to make an invisibility spell, but is having not much luck, as she is missing an essential ingredient - a spot from the tail of the Loch Ness monster. Elspeth and Angus go and call on Ferocious-Ness, who gives them a spot from his arm. The witch tries the potion but finds that only her bottom half disappears, as the spot wasn't from the tail. She decides to give up on magic and tips her cauldron over, the liquid pouring into the loch. Thirsty-Ness appears and having drunk the water promptly disappears - well half of him anyway!