Out from the pack came a greenish bottle, full of greenish liquid. Benedick held it like a green duck egg, like a handful of precious emeralds. “This medicine,” he said, “will cure coughs and colds and collywobbles. This medicine will heal hives, hiccups and whooping cough!”

Despite a magical medicine of fabulous price, Benedick’s father died of the purple plague. Now Benedick travels from town to town selling cures and potions – a dangerous business in a doubting world.

His moatwater marvels seem doomed to end in disaster – until he meets a canny princess and someone he recognises…