The saga of the Deptford Mice continues in this sequel to The Dark Portal. The evil rat Jupiter has been defeated, and the young Deptford mice emerge from the sewers to start a new life in the country. But the albino mouse Oswald is seized by an illness and lies near death. His friend Audrey enlists the help of the ancient squirrel mystic Starwife, who agrees to heal him on one condition. She reintroduces Audrey to the once villainous rat Madam Akkikuyu, whose mind is now broken, and decrees that Madam Akkikuyu must stay with Audrey until she dies.

In the country, the mice find a bucolic existence, until they find themselves embroiled in a series of murders. The country mice suspect that headstrong city mouse, Audrey, is the culprit. But the truth is far more sinister, as Audrey witnesses the return of the supernatural evil she thought had been destroyed.