I dunno how many of you outside Australia would have heard of these two books. These were serial books done by Australian children authors Paul Jennings and Morris Gleitzman, rather like Stephen King originally did with The Green Mile, as well as those serial books done in the 19th century (like Dickens did).
Wicked! has nothing to do with the book by Gregory Maguire, nor the musical. Rather, it has to do with Dawn and Rory, kid step-siblings who hate each other, but have to work together to deal with mutant worms that emerge from a gift Rory's absent father gave him, which carry a horrendous disease. It's basically Resident Evil for young teens.
Deadly! involves strange goings-on in a nudist colony, where a teenager (who adopts the name of Sprocket, the long-dead son of a hippy couple) wakes up with no memory, no clothes, and strangely adult-acting children sifting through his crap. Meanwhile, Amy suspects her father, a plant geneticist, of having an affair, and tries to get enough evidence to confront him and tell her mother, only to find he was engaged in experiments related to the nudist colony. Oh, and she is saddled with a baby girl that she thinks is her father's lovechild. At stake is a strange plant that makes a special tea, and the nudists will do anything to get it germinated again. I swear I am not making this up. Deadly! is the better of the two.