Tarot is saved from being burnt at the stake by the Roundheads, but Thalia and Dalbiac are waiting with more nightmare gas. And this time there's no escape.

A diamond that can turn people in to chalk; a talking computer and an eccentric chess master called Ceribraun involve Tarot in a new and interesting mystery.

Ceribraun's trap for Tarot is well baited - with Mr. Sweet! But when it appears that the Eye of Ra has turned Mr. Sweet into a tiny chalk statue, Tarot, Lulli and Sam decide to act