Nick and Sally are pretending to be The Cat in the Hat. But there's only one Cat, no doubt about that! Pretending to be other people is hard. The Cat takes Nick and Sally to meet his good friend Mimi the Mimic Octopus to learn some tips on how to pretend to be someone else. They learn how to observe, pick out something special about the person and then copy it. Mimi does it to protect herself, but now Nick and Sally can pretend to be the one and only Cat!