From the outside, 5 Brocklehurst Grove looks like an ordinary house - the windows are always clean, and the garden well-tended. And from the inside, to hear the voices of the inhabitants, the Mennym family, you would think they were a perfectly ordinary family, too.
Wrong. The Mennyms - Granny and Grandpa, Vinetta and Joshua and their five children, as well as the elusive Miss Quigley and mysterious Pilbeam - are far from ordinary. The whole family share an astonishing secret behind which it's hidden for forty years, a secret to which nobody has even come close . . . until perhaps, now.
When an airmail letter from Australia comes through the letterbox of number 5, its contents are enough to plunge the whole family into fear that now, for the first time, the mystery surrounding it is about to be exposed.