The Most Perfect Thing is about how eggs in general are made, fertilized, developed, and hatched. The eggs of most birds spend just 24 hours in the oviduct; however, that journey takes 48 hours in cuckoos, which surreptitiously lay their eggs in the nests of other birds. From the earliest times, the study of birds' ovaries and ova [eggs] played a vital role in the quest to unravel the mysteries of fertilization and embryo development in humans. Birkhead uses birds' eggs as wondrous portals into natural history, enlivened by the stories of naturalists and scientists, including Birkhead and his students, whose discoveries have advanced current scientific knowledge of reproduction.