Once again, I present to you John Behr as a guide to Irenaeus, from Behr’s book Irenaeus of Lyons, p. 94:

Book Three: The Apostolic Preaching
Preface
Scripture, Tradition, Church (haer. 3.1-5)

I. One God (haer. 3.6-15)
Witness of the Prophets, the Apostle, and the Lord himself (haer. 3.6-8)
Witness of the Evangelists (haer. 3.9-11)
The other apostles (i.e. Acts) (haer. 3.12)
Supplementary comments on Paul (haer. 3.13-15)

II. One Lord Jesus Christ, the Saviour (haer. 3.16-21.9)
The witness of the Evangelists (3.16.2-5)
The identity of Christ (haer. 3.16.6-18)
The ‘signs’ of Salvation (haer. 3.19-21.9)

III. Recapitulation of Adam (haer. 3.21.10-23)
The Church as the locus for the human being (haer. 3.24-25.6)

Conclusion

Behr writes:

Book three is thus structured in the same threefold pattern as book two, demonstrating that there is one God, one Christ revealed in what he has done in the one economy, and the new reality that this recapitulation has brought into effect, providing a new head for those who turn to Christ.