Sinister old women are a staple of children's stories - who can forget the terrifying scene in Disney's Snow White when her stepmother transforms herself into a hag with a poisoned apple? Yet old women can be not only powerful but also a force for good - and fun. Two new novels, one for teenagers and the other for 7+, play with these ideas.

Sarah Singleton is outstanding at creating creepy magical settings, and the Poison Garden of the title is one of seven created by the Guild of Medical Herbalists. Thomas discovers this when he inherits a magical box from his dead grandmother, and enters a garden where her ghost tells him that she was poisoned. Her box lets him into Broceliande, the Garden of Dreams, but there are six others, congruent to six other boxes. Which belongs to his grandmother's murderer? Who is the sinister man trying to gain possession of all the boxes? Who paid for each murdered person to have a violin played at their funeral? Thomas lacks definition and individuality as a hero, but the world he enters is so richly fascinating that the reader is swept along.

Apprenticed to a master chemist, Thomas soon meets the other members of the guild, an eclectic bunch of witches that includes one other child - the pale, doll-like Maud. She takes him into the Poison Garden, where every plant brings death - but does she control it or does somebody else? Singleton's Gothic imagination works wonderfully in a story that is set in the late 19th century, but which is timeless. Are the seven gardens real or imaginary? Are they the product of magic or a kind of superior alien technology? Like all Singleton's fiction, this treads a fine line between fantasy and philosophy, and will be particularly pleasing to readers of 11+.

Kaye Umansky's witch, Pongwhiffy, is 21 years old - though her habits, which make her as appealing as Horrid Henry crossed with Winnie the Witch, are unchanging. Eating skunk stew and guzzling toffees while her poor familiar, Hugo the hamster, does all the housework is the least of it. Even Pongwhiffy begins to realise that life can't be all sweets and sloth, so in a burst of determination she commandeers the Royal Gardens and a TV star and ropes in assorted inhabitants of the Wood for the O'Lumpick Games.

There are lots of heavy-handed jokes (a vampire called Vincent Van Ghoul, a goblin called Plugugly and a giant baby) that will give primary-age children the giggles. Regrettably, the book shows signs of having been written quickly, but it's genuinely amusing since children will spot how closely Pongwhiffy resembles the kind of middle-aged schoolteacher we all half-love and half-loathe.

The Poison Garden by Sarah Singleton (11+)
Simon & Schuster, £6.99, pp 284 Buy the book

Pongwhiffy Back on Track by Kaye Umansky (7+)
Bloomsbury, £5.99, pp232 Buy the book

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