It follows Arthur Penhaligon, a twelve-year-old boy who discovers that he is the heir to an otherworldly House and must fulfil a mysterious Will in order to claim it from seven antagonistic Trustees.

Twelve-year-old Arthur Penhaligon is experiencing a severe asthma attack at school when two mysterious men, Mister Monday and his butler Sneezer, appear in front of him.

Leaf confirms that she also saw Monday and Sneezer, and Ed adds that they saw dog-faced men digging up the school field looking for something.

Without help of the Atlas, Arthur attempts to navigate his way through the Lower House, which he discovers is a fragment of a world unto itself, around which the Universe is organized, created by a divine being called "the Architect."

On his journey, Arthur is attacked by a group of Nithlings, creatures born from Nothing, but he is saved by a Cockney girl named Suzy Turquoise Blue, an agent of the first fragment of the Will.

While in the cellar, he meets a Denizen called Prauvil, who later betrays Arthur, for he is secretly an agent for one of the Morrow Days, Superior Saturday.

Arthur decides to use the First Key to heal Mister Monday from his affliction of Sloth, before turning governance of the Lower House to Dame Primus.

Arthur receives a cure for the Fetchers' disease, as well as a telephone to use in emergencies, and returns home, relieved that his adventures in the House are over.

[7] In 2019, Deadline reported that Herschend Entertainment Studios purchased the film/television rights to the Keys to the Kingdom series, with Nix to serve as an executive producer.