The first edition of this book can be hard to identify because it is undated. It is bound in black and has a crest about one third of the way up the spine There is no catalogue at the rear and no other titles by W.E. Johns are mentioned in the preliminary pages. The early editions contain no colour frontispiece but have 17 black and white illustrations by Johns. There is also a distinctive error in the text which occurs in the first three editions, on Page 224 of the story "THE FOG!". The code number of the spy is given incorrectly as "2792" when it should be "2742".