Set during September 1949, confusion reigns when St Swithin's Girls' School is accidentally billeted at Nutbourne College: a boys' school. The two heads, Wetherby Pond (Alastair Sim) and Muriel Whitchurch (Margaret Rutherford), try to cope with the ensuing chaos, as the children and staff attempt to live in the newly cramped conditions (it being impossible to share dormitories or other facilities), and seek to prevent the children taking advantage of their new opportunities.