Story - Vanishing Act.
Fandoms - Jonathan Creek, Harry Potter, The Secret World of Alex Mack
Teen, no warnings.
I've just posted a story called Vanishing Act on the Buffyverse crossover site Twisting the Hellmouth - https://tthf.me/kl7K
This is basically a Jonathan Creek mystery in a world with superheroes, the main fandoms being Jonathan Creek and an AU non-magical version of Harry Potter - and bits of several other fandoms including Stargate and Buffy.
I won't be posting it here because it's set in the Teraverse, a hugely complicated multiple crossover setting created by Diane Castle which must be getting on towards three million words by about twenty authors - the bits you will need to read for it to make any sense, at a minImum, are the first, third and possibly fourth stories of this series: A Brane of Extraordinary Women - together they're about 2 million words! I think it's a fair assumption that most people who read this will already be familiar with this setting from having read these stories over several years, so I'm not going to try to explain it here.