It is the one day in the year that Clarissa really fears - the wedding anniversary of their next door neighbours, the Sopersteins. Why? Because Clarissa gets to babysit their daughter, little Elsie Soperstein. Clarissa is almost out of the door when the phone rings and she answers and tells Edna Soperstein that she won't be able to babysit Elsie this year. All appears to be going well until Edna comes to the door just as Janet and Marshall are going out, and Clarissa's cover story is blown by Ferguson. Reluctantly, Clarissa and Sam are trapped into babysitting the horrendous eight year old. After a row of defeats, Clarissa enlists Ferguson's help in dealing with Elsie but even he quits when Elsie starts professing undying love for him. Eventually Clarissa and Ferguson work together to ensnare Elsie and then blackmail her into behaving.