Maggie and Bernard have discovered the missing link gene which gives humans the ability to reason and speak. They set up a self-sufficient community in the north of Scotland and successfully implant the gene into a number of animals and birds. In addition, they find they can do the reverse: seed their unborn children with animal genes to give them, for example, the agility of a frog or the ability to swim like a dolphin. Given the uniqueness of this gene, they believe that it was implanted in mankind by an alien. In an African cave Bernard and his 10-year-old son Colin discover a picture which leads them to Tibet and the last remaining Yeti.

As the social, economic and military situation in the world worsens around them, Christie, (Maggie’s 13 -year-old son), and Bernard unwittingly unleash a strange being from a stone which the Yeti gave to Christie. They realise that this being is the alien which originally gave humans the missing link in order to enable us to reach a level of technology it could use to return home. Now it intends to remove the gene from all humans by means of a worldwide virus.

For all they turn on some far-reaching topics, the books are relatively gentle in style. There is little grittiness about them as Christie is easily shocked by the failed results of former experiments preserved in Maggie’s underground lab, and shies away from discussing the delicate question of how Maggie has introduced the various animal gene into her unborn children. The books are so easy to read that it is worth bearing in mind the potentially serious nature of the subject matter being discussed.

Set in the near future, the books have a faintly apocalyptic air. From the first, the developed world is in economic and social turmoil. There are chronic fuel shortages, leading to civil unrest and, later on, to an effective abdication of power by the central government which has granted itself an extensible term of office. Aside from the initial journey the children make from Ireland to Scotland, the outside world is background noise. Their community is self-sufficient, growing enough food to feed humans and animals, relying on wind, water and solar power for electricity, and to some extent able to defend itself against attack.

The two scientists, Maggie and Bernard,have a compelling attraction about them. They have created a pleasant community in which talking and non-talking animals and humans peacefully coexist. Their scientific achievements are impressive. However, ethically, they are outside the pale. They test their theories on their own unborn children, effectively reducing them to experimental subjects rather than living autonomous people. We know of one dead newborn child, preserved as a reminder of failure. We do not know how many other abortive attempts there may have been along the way. Maggie responds to accusations by saying, “Some say that we’re interfering in a process that has always been taken care of by nature; or by God, if you prefer. … What we’ve done here may be unethical… One of the reasons I’ve been able to live with my conscience is that neither I, nor Bernard, has ever looked for any profit from anything we’ve done.”

At the heart of the whole series is the difference between animals and humans. Although this difference is explained away by the presence or absence of a specific gene, Christie spends time musing on whether we might not be better off if we were like the animals, i.e. carefree, loving and so on. At some point Christie and Bernard discuss whether or not giving intelligence to the animals might not have been a mistake, on the grounds that all we have done with our own intelligence is to start wars and to kill each other. It is almost as though the issue is brought up to satisfy would-be critics, but immediately avoided.