David Gallaher and Steve Ellis's series - based on the 1940s' radio serial - was originally produced exclusively for ComiXology's popular iPhone application.
The series follows Dan Holiday, an investigative author who is sent on a journey of discovery after finding a mysterious box left on his table after a signing.
"There is gunplay, conspiracy, romance, psychological drama, train chases, motorcycle chases, and danger," Gallaher told CBR. "But, at its heart it's a story about rediscovering your place in the world after everything in your life changes forever."
Gallagher and Ellis were the first winners of DC imprint Zuda Comics' monthly webcomic competition.
Box 13 will be previewed in Red 5's Free Comic Book Day issue on May 1, with the complete graphic novel arriving in shops on May 19.