Listen to Shadow Planet!

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.

Get the book

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 Gernert, took the book to the world.

July 2021, Berkeley

The main thing to do here is sign up for my email newsletter, which is infrequent and wide-ranging. I always try to make it feel like a note from a friend: