A cartoon-style adventure with cats for people. Feeling baleful about her family's preference for her model older sister, Violet goes off to play at the dump, where she finds a cape that transports her, like Superman, when she says the magic words: ``I am Violet!'' Next, she happens on a pleasant character called Grim who says he's a robber. He does have a packful of cash, but the rest of his story is the product of his colorful imagination. Real robbers turn up; with Grim's help, Violet thwarts their next heist with bravado and ingenuity. A lively romp, well-paced and funny. Illustrations not seen. (Fiction. 7-10)