A Treatise on the Justification by Faith by Archibald Alexander
This 95 pg. affordable paperback has 12 complete chapters and four follow-up check-ins to see where your Faith is: One; The importance of salvation, two; The Refudge of Lies, three; Evidences of a New Heart; and four; The Cross. 
The books' main burning question is how this doctrine must be rightly set forth. The Christian Faith rises or falls based on this doctrine. It holds firmly to our foundation of how man is Justified. What justification is and what it is not.
The book review written on the back is by long-time friend Jon Eskola, elder in the Grace Reformed Church. An incomplete book list is within the book.