Review: The Humans, By Matt Haig

A Vonnadorian assassin's guide to Planet Earth

Mission impossible: the lone alien soon finds himself warming to the humans he has been sent to kill (Getty Images)

Matt Haig's new novel, his fifth for adults, is a wryly humorous look at the human condition as seen by an alien. The narrator comes from the planet Vonnadoria, where life is based around maths, logic and rationality, with no messy emotions to clutter up the immortal existence. So far, so Mr Spock, but the interest comes from the narrator's mission. A professor of maths at Cambridge University, Andrew Martin, has solved the Riemann hypothesis, a real mathematical conundrum involving prime numbers. Vonnadorians believe that this holds the key to space travel, so the narrator's job is to exterminate Martin and anyone to whom he has divulged his discovery.

At the beginning, Martin has been killed, and the alien is inhabiting his body. The fun starts immediately: while the alien can absorb vast amounts of theoretical knowledge about humans, their illogical customs are harder to learn.

Of course the plot is allegory for how our highly technological but often inhumane culture, with its inherent paradoxes, seems to an outsider. The themes are sometimes obvious if heartfelt: "They can drive a car 30 miles every day and feel good about themselves for recycling a couple of empty jam jars. They can talk about peace being a good thing yet glorify war." But they are often wise: the facades humans use, like avoiding talking about the issues they want to discuss; or the masks of social politesse, or their intolerance of difference: "Maybe this was another human trait. Their ability to turn on themselves, to ostracise their own kind."

Haig, who has written eloquently about his own experience of depression, and who mentions his period of suffering panic attacks in an afterword, is sensitive on the way that a supposedly advanced species treats its mentally ill ("sadness seemed to me like a disease, and I worried it was contagious"), and on shortcomings of medicine such as the absolute separation of illness of body and mind. There are sharp gems: "Humans ... don't like mad people unless they are good at painting, and only then once they are dead." And droll observations on other topics abound.

The alien starts off determined to carry out his commands, but finds himself falling for some of these beings, despite – or perhaps because of – their foibles. In particular, he finds ways of avoiding his orders to kill Professor Martin's beautiful but beleaguered wife and her troubled son. This process allows Haig to explore emotions and the risk of vulnerability and pain that they bring.

There are a few blunders. The alien mentions the presence of hydrogen in air as a constant, but air doesn't contain pure hydrogen. Water vapour contains hydrogen, but as part of a different molecule. The alien is also flummoxed by metaphors, but in between being bewildered by "big fish in academic circles" and "right as rain", he himself uses a metaphor: "My task was going to be easy ... the meat of it", and later reads "between the lines".

Cynics may consider some of the listed advice given by the alien to Professor Martin's son to be homilies. But that is missing the point. This is a tender, funny novel about the often irrational ways humans behave, written in accessible prose, and invites comparison with Mark Haddon and Patrick Ness.