It might be always sunny in Philadelphia, but that doesn't mean there aren't some clouds about to hit Abbott Elementary school. A major crossover event kicks off on Wednesday's episode of Abbott Elementary,

Spoilers for the Abbott Elementary and It’s Always Sunny in Philadelphia crossover are ahead! If you haven’t watched the first half of this event yet, you can stream the Abbott episode with a Hulu subscription.

Here's some background and inside jokes to help fill in some of the gaps for viewers who don't watch both Philly-based shows.