Cosmo and the Great Witch Escape by Gwyneth Rees

Cosmo, a witch-cat, is delighted that evil Sybil – the most terrible of witches – is safely in prison. In fact, she’s even fitted with a special tag, which means that if she and her cronies try to escape they will be turned into frogs. But then mysterious goings-on are reported in Witch News. …  Cosmo and the Great Witch Escape by Gwyneth Rees