William is young, unemployed and bored. Life in seventeenth century London is not well-suited to him, nor he to it. But after Mr Flowers falls into a swoon at the serving of a custard, William's destiny is revealed: a quest for perfection. In custard. Should William succeed, he can lay claim to Mr Flowers' fortune. William desires not only to save his father from the debtor's bench, but also to fill his empty days and the hole in his heart left by the departure of his beloved friend, Ferdinando. Most of what William has so far learnt in life is from books, so this is where he begins. It soon becomes clear that an ability to boil mice is of limited use.

The story of William's quest is one of astrology and alchemy, cooking and hairdressing, and of young men with exotic tastes in dress. But most of all, it is the story of custard.