Three of these novels explore human identity in a modern world threatened by change. Only Human (a sequel to The Missing Link) is concerned with genetic modification and its possible effect on humans: implant experiments have given dolphin genes to Danny and the muscle tissue of a frog to his sister.

Here, narrator Christie (“only human”) and his oddly assorted companions travel to Tibet to find the yeti, which Danny’s father, Bernard, believes holds the “missing link” of human evolution; in a parallel story, Danny finds kinship with mer-folk. Did early extraterrestrials know the secrets of DNA? Will cloning save the yeti from extinction? Christie questions Bernard’s motives, especially when the frog-daughter is rejected as a monster. The strands of the plot are cleverly linked in a story full of appeal to readers of about 10 and above.

In The Beguilers, for slightly older readers, Kate Thompson plunges us straight into the ways of an imaginary society. Convention and caution are prized, independence is regarded with suspicion.

Rilka finds herself at odds with her elders and doomed to be an outsider when she decides to catch a “beguiler” - one of the Siren-like spirits which haunts the mountains. Much safer are the “chuffies” - endearing, snuffling creatures which sense human sadness and take the role of companions - but Rilka finds that beguilers and chuffies are linked. This fantasy world is vividly drawn, and the reader becomes knowledgeable about its vegetation: druze bushes induce dangerous lethargy, while jub-nuts boost energy.

Thompson hasn’t avoided the pitfalls of the quest novel: Rilka’s solitude leads to a sameness of pace, and it’s difficult to feel excitement about the outcome.

Human replicants appear in many a science-fiction film, with plot possibilities springing from the protagonist’s inability to know whom to trst. In The Angel Factory, 12-year-old Tom Wisdom discovers that his parents and sister are “angels” - benign extra-terrestrials bent on saving Earth from self-destruction through “the Project”.

Spying on his family, Tom learns that he was adopted as a baby and chosen as an experimental Project child. Terence Blacker’s plot has surprises as more angels reveal themselves, but the most poignant element is “the Tom and Gip Combo”, Tom’s friendship with an eccentric, single-minded schoolmate. Armed with knowledge that could endanger the Project, Tom acknowledges that to be human is to be unpredictable, irrational and often wrong, but that these liberties must be preserved. This is a riveting fantasy adventure with a solid basis in relationships.

Weather forecasters who apologise for the “risk” of a shower might do well to contemplate Ultraviolet, Lesley Howarth’s bleak vision of the near future in which the outlook is “sun, sun and more sun, I’m afraid”. The sun’s rays are so dangerous that humans live behind screens and in tunnels hollowed beneath desert wastes, and only for three midwinter months is it safe to venture outside.

Violet (Vi) and friends, drilled in “sun manners” and subject to radiation checks, make illicit excursions between bouts of immersion in virtual reality games. Vi is caught between separated parents: scientist father, developing the protective BluScreen that Vi thinks should be available to all, and TV journalist mother.

Howarth’s style is distinctive and her inventiveness is admirable, but it’s difficult to engage with her characters; everyone speaks in the same clipped dialogue. But, in twist after twist, we emerge from levels of the fantasy game to what we think is reality, in an imitation of Vi’s experience.

As with many futuristic dystopias, the main interest is in the detail of how the world is organised rather than in the somewhat confusing plot - and whichever version is “real”, the visions are frightening enough. Ultraviolet should be compulsory reading for world leaders, especially presidents of the United States.

LINDA NEWBERY