Tom Natsworthy, an orphaned History apprentice on the Traction City of London, is sent in disgrace to the city’s Deep Gut after a bullying fellow-apprentice taunts him into a fight. There he encounters his hero, the historian-explorer Thaddeus Valentine and saves him from a murderous attack by the strangely-scarred Hester Shaw who then escapes, wounded, by dropping down to the ground beneath the city. Valentine pushes Tom after her and London leaves them behind. Forced into an alliance of necessity, Tom and Hester follow on foot but are quickly caught up in a world of airship aviators and the mystery of why Valentine killed Hester’s parents and left her for dead, badly wounded. Welcome to our world, but so far ahead that the characters’ distant past is our distant future.

This is the canvas on which Philip Reeve has painted the world of the Mortal Engines quartet. In many respects it’s a much less technological world than our own, largely the result of one particularly devastating conflict: the 60-Minute War which left vast areas of the planet uninhabitable. Since that time, empires have risen and fallen and the debris they left behind is plundered by explorers for Old Tech to supplement their effective but limited technology. Two technologies dominate: land-crawling traction cities; and sophisticated airships. However the author isn’t so much interested in the mechanics of a fictional time and place as in its use as a backdrop for a human story with a more-than-slightly Edwardian flavour to it. Why do I like the Mortal Engines series so much? Because the author depicts a world which is both recognisable and imaginatively different. He populates it with characters who are intelligible but not two-dimensional, complex but not irritatingly so.

I have some reservations about certain aspects of the series; not many, but enough to prevent my recommending it one hundred percent. Nevertheless this is an enjoyable, engaging and mostly wholesome series for young teenagers. Tom is an idealist, an historian by training, orphaned when his parents were killed in an accident. He is inclined to think the best of everyone and is concerned and compassionate. Hester is mistrusting, embittered, solitary and ruthless, but she comes to love Tom fiercely. She harbours a hatred for Valentine who killed her parents and left her brutally scarred, and she is devastated when she discovers that he is her biological father. This relationship haunts her throughout the books and she keeps it a secret from Tom who is horrified when he discovers how readily she kills people. The two of them make for fascinating characters, vital and strongly marked, deeply in love with each other in spite of their many differences.

I must admit to being pleasantly surprised by the presence of religious belief in the series as a whole, and of the positive effect of Christianity in the final two books in particular. Religion rarely gets much of a fair deal in sci-fi. There is a sour note in the final act of the saga which disappointed me and which was only partly counteracted by the definitely hopeful epilogue. Tom, whose heart was weakened years before when he was shot, has used all his strength to try to broker peace. Although he succeeds, Tom dies in the attempt and Hester, unable to live without him, takes her own life. This final action is consonant with her character throughout: driven by a bitterness which is tempered only by her wholehearted love for Tom. I wish that there might have been some more redemptive outcome for her.

In the last analysis the message of the Mortal Engines stories is one of hope, hope nourished by genuine human endeavour and in some way by Christian charity and forgiveness. The whole series is enjoyable and well-paced, populated by engaging and vivid characters. I regret a very slight uncertainty over the question of Tom and Hester’s marriage, and the concession to romantic suicide in the final act. But it’s rare enough to find a story which accepts that religion has a part to play in people’s lives, and rarer still to find one in which it is the catalyst for good.

Tim Golden is a computer programmer in London.  He is also the editor of the Good-to-Read website.