Marcus Orion is an authority on the Inca and their relations to astronomy. Sadie says he wrote 'the' textbook on Inca's relationship to astronomy. Sadie tells Roland how they should contact him in New Orleans as he was referenced in correspondence with her father, Henry Keating.
- Henry Keating's correspondence has a picture of Marcus when he was younger. Though his age is unconfirmed, Roland points out that at the time the photo was taken, Marcus, 'wouldn't have been much more than a boy in your (Henry Keating's) time, surely'.