Michael Barrett's premise is simple: the Old Testament is about Christ and he can and should be found there as we read it - all the way from Genesis to Malachi.
Thus, his methodology is to first establish the Person and Work of Jesus Christ, as presented in the New Testament, then as we read the Old Testament, Christ is identified as the fulfilment or reality of Old Testament hints, clues or shadows.
In Part 1, he asks: Whom to look for? He then provides us with quite a comprehensive study on 'Messiahship' (Chap. 1), Jesus' Person (Chap. 2) and Work (Chap. 3).
In Part 2, he asks: Where to look? Barrett suggests that we can see Christ in the covenants (Chap. 4), in person (Chap. 5. He deals with Christophanies here), in His names (Chap. 6), in word prophecy (Chap. 7), in picture prophecy (Chap. 8-9. He spends quite a lot of time on Typology), and in song (Chap. 10).
In Part 2, he essentially looks at texts/passages that lend themselves quite easily to Christological interpretations, and although those are helpful insights, I would have preferred if he dealt with the Old Testament on a larger scale. I'm thinking about how books point to Christ where there is seemingly no mention of him - for example, Esther and Ecclesiastes. However, he does manage to cover a wide range of topics, themes and passages and perhaps me asking for more is unreasonable.
I must admit that I struggled through certain sections of the book - perhaps I wasn't used to his writing style - but that overall, the argument of the book is lucid and structured clearly. This is a good book to read if one wants to learn principles to find Christ in the Old Testament. I wouldn't agree with all of his points, but he does model a Christological reading of the Old Testament.
For a different way of finding Christ in the Old Testament, I would suggest Sidney Greidanus' "Preaching Christ from the Old Testament."