Diana Wynne Jones’s books are instantly identifiable: they abound with seemingly chaotic but actually well-structured plots, dazzlingly zany imaginative locations and characters, and a sense of deep wisdom and love for one’s fellow man. Her posthumous novel, The Islands of Chaldea, has been finished by her sister, Ursula Jones, in a manner so unobtrusive that it is nigh on impossible to spot where one Jones ends and the other begins.

Set in an alternative Britain, where the four countries (known here as Skarr, Logra, Bernia and Gallis, each with their own magical totemic animal, from Logra’s bull to Gallis’s lizard-dragon) are contained not only by seas but also by a strange magical wall, this is a skilful and poignant account of the need to overcome barriers. Many of Wynne Jones’s favourite themes occur here: journeys, reunited lovers and kingdoms, enigmatic spirits and, of course, quirky, mettlesome young men and women. Although I came late to Wynne Jones’s work, I still, as an adult, find in it a distinctive sense of bittersweet wonder that, given this is her last, remains all the more powerful.

Tale of a Tail by Margaret Mahy is also, sadly, posthumous. Mahy wrote some of the most original children’s books of the last few decades and this little book displays her talent for the rumbustious, the comic and the magic that is found in the everyday world: ‘Do you ever think about – about ordinary things?’ asks Tom, the hero. ‘I mean how strange they really are.’ He’s quite right, of course, and that’s even without the wish-granting dog that he stumbles across, whom children of eight and up will adore.

A darker, wilder kind of magic is present in Catherine Fisher’s The Box of Red Brocade, which continues the story set up in The Obsidian Mirror. Mortimer Dee’s scrying mirror acts as a portal between centuries and even dimensions: a tyrant from the future, a medium from the 19th century, rebels, elves and adventurers all want to get their hands on it – and keep it from falling into the wrong ones, which it sort of already has. Fisher’s prose is keen, sharp and bright as berries, and the pace of this thrilling instalment will keep eleven-year-olds and their older siblings gritting their teeth with excitement.

Time travel of a different sort is present in Sonya Hartnett’s superb The Children of the King. During the Second World War, Cecily and her brother are sent, Narnia-style, to live with their uncle: only this one’s very glamorous as well as intelligent and the other world that they come across manifests itself in the ghosts that haunt Snow Castle – but are they really ghosts? Hartnett is a writer of assured clarity, evoking bored, aristocratic mothers, the terrors of the Blitz and the manners of the children who may be the Princes in the Tower with verve and style. Highly recommended for those who are eleven and above, it concerns dreams, power, glory and friendship, and ought to win every prize going. (Hartnett had my old, soft heart breaking: I wept for the entire last chapter.)

Mary Hooper’s Poppy is a vivid and involving account of a VAD nurse in the First World War and her love for an unsuitable, toffish cad. Hooper writes with a fine and sensitive understanding of her young heroine, thrown from maiding in a country house to nursing soldiers: from one form of drudgery to another, only now Poppy must re-evaluate the role of women and her own place in society in order to face the terrifying, exhilarating future.

The Interregnum is not a time period that many children’s books have approached: Sarah Naughton’s second novel, The Blood List, sees Cromwell as a distant figure, in this tale of Puritanism and witchcraft. Barnaby, the blond and uncomplicated son of the local squire, hates his pious and secretive brother; when the latter accuses him of consorting with the Devil, Barnaby is catapulted into prison and awaits certain death. Gripping and beautifully wrought, it evokes the mounting fear in a small village with glee.

There is a moving story in Virgil’s Aeneid of two young soldiers (and lovers), Nisus and Euryalus, one of whom is slain on a night raid. It’s poignant and exemplary of the charm and doom of youth. Caroline Lawrence, in The Night Raid, has produced a solid retelling for dyslexic teenage boys. Nisus and ‘Rye’ are given back stories; the homoeroticism of the original is absent. Though the book can feel a little clunky, that’s very much to do with its target market, and it has a great deal of raw power. There’s a lovely scene at the end, where the ghosts of the pair meet Virgil and thank him for making them immortal (rather like the beginning of Ursula Le Guin’s Lavinia, where Aeneas’s wife stumbles across the shade of Virgil in the forest; only there he’s upset, as he’s got her hair colour wrong).

Dublin is the backdrop for Roddy Doyle’s Brilliant, in which a black dog – that of depression – is stalking the streets. Only the children (with the aid of talking seagulls, meerkats and owls) can stop it. There is a manic energy to this engaging story, which takes place over one night only, and shows how the most terrifying and enormous monsters can be defeated solely with what are apparently frail weapons.

Two slickly moulded thrillers show children coming head-to-head with the adult world: Martyn Bedford’s Never Ending, a sophisticated account of how a teenage girl deals with the death of her brother while on holiday; and Kevin Brooks’s The Ultimate Truth (Macmillan 320pp £6.99), which likewise sees a boy investigating the death of his parents in a car crash. Bedford engages successfully with the teen psyche and deals sensitively with his troubling subject matter, while precisely evoking family dynamics and the sweltering confusion of adolescence. Brooks’s book concerns a complex world of spies and double agents, hurling a thirteen-year-old boy into ever more engrossing and bewildering situations. Unlikely alliances and double-crosses are manifold.

They also appear in Matt Haig’s Echo Boy, where immortality is creeping up on humankind. It’s set in a very convincing near-future, where most of the world is either underwater or scorching; ‘mag-rails’ mean you can travel anywhere at vast speeds. Everyone has an android known as an echo; when one kills the heroine’s parents, things quickly move out of control. Echo Boy is fast-paced and clever, and teens will wolf it down. For me the most frightening thing wasn’t the huge corporations, or the robots coming to life; it was that in this future, writers and journalists have to work entirely for free.