Mr. Penumbra's 24-Hour Bookstore

An unemployed graphic designer who takes the overnight shift at Penumbra's bookstore and slowly uncovers the secret society behind its strange customers.

The society's "First Reader," an old-guard leader deeply suspicious of using modern computers to crack its ancient code.

The bookstore's elderly, enigmatic owner, and a member of a secretive society of book-obsessed puzzle-solvers searching for immortality.

A Google engineer who becomes Clay's love interest and brings modern data analysis to bear on the bookstore's centuries-old puzzle.

Clay's wealthy childhood friend, a tech entrepreneur who helps fund and support the investigation into Penumbra's secret.