Our month with St. Justin was really great. I learned a great deal from it and I'm very much looking forward to our month and a bit with St. Irenaeus starting today. Five chapters per day (each chapter is brief) will have us finished Book One by Wednesday, 12th May.
St. Irenaeus, Against Heresies, Book 1
Or this pdf version with Ante-Nicene Fathers footnotes included.