The Cascade is an obscure event in the history of the PPC, roughly the mid-1980s HST, in which the young Makes-Things caused a chain reaction of plothole formation which spread throughout the Multiverse. The nature of the Cascade plotholes led to HQ's connection with various areas of canon locations, such as the Shrieking Shack and a mountain range in Arda, and the network formed was used to rapidly expand Headquarters. The various far reaches of the plothole network were kept in check by HQ's shields, but the failure of those shields can allow bits of other worlds to enter HQ, which could potentially lead to a collapse of the entire complex if left unchecked. The shields have been known to have gone down twice: during 2006, which allowed the Black Cats to invade, and during 2013, when their failure was a direct result of the Blackout.
After the Cascade, Captain Dandy and the Weeds were sent by the other Flowers to explore the newly expanded plothole network. The Weeds were lost for years, only brought back out of hiding by the Sub Rosa after the Reorganisation when they were tracked down to form the Department of External Security.