The Deptford Histories, book 1: The Alchemist's Cat
Robin Jarvis1994

The year is 1664 when young Will Godwin comes to London. In order to survive, he becomes an assistant to a wicked alchemist, Elias Theophratus Spittle. On an errand one freezing night, Will finds a mother cat and her three kittens, and brings the family back to his master's lab. Among the bubbling bottles and evil smelling jars of his master's apothecary shop unfolds an extraordinary tale of villainy, sorcery, and murder. The Deptford Mice trilogy witnessed the harrowing battles between the mice of Deptford and Jupiter, lord of darkness and treacherous disguises. Now in this gripping prequel, Jupiter's secret history is revealed.