You should read Redemption Accomplished and Applied by John Murray.
It is a great and short (though somewhat thick) treatment of the atonement.
Part I deals with “Redemption Accomplished” — what Christ actually accomplished on the cross. Part II deals with “Redemption Applied”, dealing with the order, content and benefits of redemption.
I don’t agree with every jot and tittle of Murray’s perspective, but, overall, this is a great treatment from a great theologian. One thing I particularly appreciated is Murray’s emphasis on union with Christ. He says that “it underlies every step in the application of redemption” (161).
Murray’s style is not light, and neither is the subject he’s writing about. I would recommend reading a chapter a day for two-plus weeks, and letting each truth sit for awhile. There are 15 chapters and 181 pages in this book. That is about 12 pages a chapter. Take about half an hour a day, and really soak yourself in the great truth that this book expounds.