The core of The Coiled Spring consists of six chapters, two on each of fruit flies, vertebrates, and plants. The first chapter in each pair covers the determination of the primary axes in embryos (how animals initialise their anterior/posterior and dorsal/ventral structure, and plants their apical/basal and radial patterning). The second looks at the formation of appendages — wings and eyes in flies, limbs and eyes in vertebrates, and flowers and leaves in plants. Bier makes no attempt to be systematic here, instead using a few detailed examples to explain the basic mechanisms involved — division into increasingly specialised domains, morphogens and induction, autoactivation, mutual inhibition, and so forth.
The details in all of this are superficially intimidating, with lots of strange gene names (sonic hedgehog, pax6, agamous, and so forth) and other specialised terminology (mesoderm and ectoderm and endoderm, organizers and neuroblasts, marginal zones and meristems, and so forth). But the key ideas are not that difficult and they are explained multiple times in different contexts. In addition to an overall glossary, lists of key terms and important genes accompany each chapter. The Coiled Spring also has exceptionally clear colour diagrams (as well as a couple of pages with small photos from actual experiments). Bier has a fondness for analogies with household electronics, which are interesting if not always helpful. He also includes almost a score of "bioboxes", with a page or two on the careers of key biologists involved with developmental biology; these are professional rather than personal.
The Coiled Spring doesn't look at all at later stages of development, but it does cover the fascinating evolutionary angle in some depth. Vertebrates and invertebrates share a common developmental inheritance — only a decade ago it was discovered that some vertebrate homeotic genes can even substitute for fly ones! And from a comparative analysis we can deduce that their last common ancestor probably had "a well defined head and tail", "repeated segments", "basic tissues types", "some kind of appendages or outgrowths", and "a light sensitive organ". There are also connections between plant and animal development, though these may result more from general constraints on the mechanisms available rather than direct common descent.
A final chapter looks at some of the broader implications of advances in genetics and developmental biology. Health and medical improvements are what spring to mind, but Bier stresses the effects on agriculture and other forms of plant production (and he gives his own take on genetically modified organisms). Heading more towards science fiction, he considers the possibilities of Jurassic Park style revivals, crossing species, and targeted evolution.