The Starflash Opal

Zophenas is an enchantress but is trapped in the Underearth. How can she escape? She has heard of three possible ways; to find the soul of Waldo the warlock, to secure the magic ointment made by a witch, enabling her to fly and to capture a woman who has turned into a two-tailed cat.
For these tasks she recruits two schoolchildren - Swot, with a gift for maths and his sister Gemma. They find Waldo, who recalls hiding his soul in a bird. But which one? They retrieve it but the ointment - guar...