Sidekick: The Tale of Billy the Kid and the Giants of Colorado - The Mythic West, #1

The Jotunheim giants poured through the rift at Andersonville and annihilated both the Union and the Confederacy. Only the desperate efforts of a few heroes stopped them in the West, at the battle of Golden City, Colorado. Those heroes became legends. Billy McCarty watched those heroes win the battle. He grew up reading the dime novels and dreaming about being like them. So when Giant Killer Cassidy came to town, Billy swore he'd join Cassidy's team.
No longer a kid, he'd do anything to be by Cassidy's side. But "anything" could carry a high price, in both blood and honor. A high price he might have to pay repeatedly. In the Mythic West, where gunslingers battle monsters of nightmare, Sidekick follows the epic adventure that began a hero's rise.