This book really eases you into the strange and difficult field of string theory, but only if you have the background, this is not a popular science book! The background is differentiation, integration, ordinary differential equations, partial differential equations, classical mechanics, quantum mechanics, a little quantum field theory, and special and general relativity. the books i reccomend to get this background, if you dont have it, are:
1) Engineering mathematics, K.A Stroud (6th edition)
2) Advanced Engineering Mathematics, K.A Stroud (4th revised edition)
3) Mechanics series (1,2,3&4), Douglas Quadling
4) Quantum Mechanics Demystified, David McMahon
5) Quantum Field Theory Demystified, David McMahon
6) Relativity Demystified, David McMahon
Wit the nessecary background this text is perfect to lead to more advanced ones on the subject.