The Smell of Fear case

"So let me get this straight… A mountain troll got loose in central London by stowing away in a charmed tent. It's angry from being struck with spells, and it's had a potent invisibility potion… but it won't stay hidden for much longer! […] [We] need a plan for capturing a troll. And fast!"

- Mathilda Grimblehawk

The The Smell of Fear case was an investigation conducted by the Ministry of Magic after an unknown beast that no one was able to see caused great devastation at the Leaky Cauldron, in London.

What had transpired was that wizard Percival Shacklehorn had travelled to the Austrian Alps with the intention of illegally catching a wild Graphorn. During this expedition, a mountain troll found its way into Shacklehorn's magically-expanded tent, and was rendered invisible when it broke a bottle of Invisibility Potion; similarly, Muggle monster hunter Laura Thorn, in the Alps at the same time searching for a Yeti, also wandered into Shacklehorn's tent. When Shacklehorn returned to London, he accidentally transported them both inside the tent: during his stop-over at the Leaky Cauldron, the invisible troll left the tent and wreaked havoc, later escaping to Muggle London.

The Ministry investigators from the Department for the Regulation and Control of Magical Creatures then devised a trap to catch the troll and relocated him back to the Alps; the Muggle was duly Obliviated, and Shacklehorn was severely fined.