Mr. Penumbra’s 24‑Hour Bookstore

This is my first novel, and it grew from a story posted on this very web­site into a New York Times Best Seller pub­lished in more than twenty countries.

It’s a tale of books and technology, cryp­tog­ra­phy and conspiracy, friend­ship and love. It begins in a mys­te­ri­ous San Fran­cisco bookstore, but quickly reaches out into the wider world and the shad­owed past. I talked about the ideas behind the book on NPR’s Morn­ing Edition and had a real-life bib­lio­phile adven­ture with the New York Times.

The cover, by Rodrigo Corral

In Blip Magazine, George Saun­ders called Penumbra

a real tour-de-force, a beau­ti­ful fable that is given legs by the author’s bravado use of the real (Google is in there, for instance, the actual campus) to sell us on a shadow world of the unreal and the speculative. Robin Sloan comes across as so bighearted, so in love with the world — the ancient world, the con­tem­po­rary world — so in love with love, in love with friend­ship, in love with the idea that our tech­ni­cal abil­i­ties can serve as con­duits for beauty, that the reader is swept along by his enthusiasm. It’s a lot of fun — but it’s also a pow­er­ful read­ing expe­ri­ence with a wonderful undeniability.

International editions

Penumbra is also avail­able from Harper Collins in Canada, Text Pub­lish­ing in Australia, Corbaccio in Italy, Roca in Spain, Novo Con­ceito in Brazil, Host in the Czech Republic, and other pub­lish­ers in Germany, South Korea, Finland, Greece, Israel, China, Taiwan, Turkey, and more.

Ajax Penumbra 1969

In con­cert with the novel’s paper­back release, I wrote a short prequel, avail­able as a dig­i­tal sin­gle on the plat­form of your choice. The story is set in San Fran­cisco, August 1969. A young man named Ajax Penum­bra arrives on the scene, look­ing not for free love but rather for a book: a very old vol­ume that might pos­sess strange powers. His search leads him to a tiny bookstore, taller than it is wide … 


Penumbra was edited by Sean McDonald at FSG. Lenni Wolff managed the copy-editing. Abby Kagan designed the inte­rior of the FSG edition, and Rodrigo Corral gave the book its inim­itable cover. Brian Git­tis man­aged pub­lic­ity for the FSG edition; Gabrielle Gantz and Andrea Rogoff took the reigns for the Picador paper­back. Sarah Burnes at The Gernert Company made Penum­bra possible. Finally, Rebecca Gard­ner and Will Roberts, also at The Gern­ert Com­pany, took the book to the world.

March 2022, Berkeley