Today is a special day for Conrad and Sally Walden--even though they don't think it is. It seems that Sally and Conrad, different as black and white, have pushed their single mom, Joan Walden, to the limit. Conrad's endless rule breaking has his mom seriously considering military school for her son--an idea planted by her just-this-side-of-smarmy neighbor and suitor, Lawrence Quinn. Sally, tightly wound though well-behaved, has bossed away every friend she has, and divides her time between upbraiding her brother and putting new 'To Do' lists in her junior palm pilot. And all the while their mom is just trying to keep domestic peace while balancing a successful career as a real estate agent for her germophobe boss, Mr. Humberfloob. However, on the Saturday that she is to host her company's party, Joan's preparations have fallen prey to Conrad's shenanigans. Thus, she lays down a mom-sized decree: Sally and Conrad are not to leave the house while she is at work; furthermore, they are forbidden from making a mess or misbehaving in any way. The kids are left with little to do besides sit and stare out of the window, while their babysitter, Mrs. Kwan, dozes in the den. Until their unexpected guest--a six-foot-tall talking feline, sporting a red-and-white-striped stovepipe hat--appears. The original party animal himself arrives to turn their world upside down by showing Sally and Conrad that "it's good to have fun--but you have to know how!"