The beginning of a well known book has been encrypted below. Each letter of the alphabet has been replaced by another using a simple substitution technique. For example, A may always be represented by G, etc. Can you name the book?
The piece of text is from the original book and should read:
They were not railway children to begin with. I don't suppose they had ever thought about railways except as a means of getting to Maskelyne and Cook's, the Pantomime, Zoological Gardens, and Madame Tussaud's. They were just ordinary suburban children, and they lived with their Father and Mother in an ordinary red-brick-fronted villa, with coloured glass in the front door, a tiled passage that was called a hall, a bath-room with hot and cold water, electric bells, French windows, and a good deal of white paint, and 'every modern convenience', as the house-agents say.
a has been represented by t.
b has been represented by r.
c has been represented by a.
d has been represented by i.
e has been represented by n.
f has been represented by l.
g has been represented by u.
h has been represented by d.
i has been represented by m.
j has been represented by k.
k has been represented by z.
l has been represented by x.
m has been represented by v.
n has been represented by h.
o has been represented by y.
p has been represented by j.
q has been represented by f.
r has been represented by p.
s has been represented by c.
t has been represented by q.
u has been represented by w.
v has been represented by o.
w has been represented by g.
x has been represented by b.
y has been represented by e.
z has been represented by s.
Please 
