Jake is a thirteen-year-old boy mourning the recent loss of his beloved grandfather. He is a logical thinker with a natural inclination toward exploration and the wilderness. Entrusted with a cryptic note and a leather-bound scrapbook, he approaches his grandfather's puzzle with determination and a one-track mind. Over time, he learns that sharing the burden of his discoveries with others is safer than working alone.

Wes is Jake's cousin and an eager participant in the summer road trip. Coming from a mixed-race family, he is characterized by his bright red hair and brown skin. He is athletically gifted and naturally inclined to solve puzzles like Morse code, though his bravery is tested by his fear of heights and tight spaces.

Amber is a family friend who joins the extended group for their two-month park excursion. She is of Argentinian descent, with dark skin and a distinctive purple streak in her hair. As the most practical and level-headed member of the trio, she acts as the voice of reason and uses her keen observational skills to spot details the boys miss.

Abe is a young orphan living in Colorado in 1880 who accidentally observes two men burying a heavy silver object. Having grown up in an orphanage without a last name, he seeks independence and opportunity in the wild. He creates the original leather-bound scrapbook and serves as the first protector of the silver spearhead.

Two mysterious men dressed in suits follow Jake, Wes, and Amber through Rocky Mountain National Park. They track the children up the Twin Owls rock formation, attempting to intercept whatever artifacts the kids uncover.

Jake's late grandfather is an avid explorer and nature enthusiast. Though deceased before the story begins, his preparation shapes the entire narrative. He meticulously planned a ten-park road trip for his family and designed a complex puzzle to test Jake's curiosity, resilience, and willingness to rely on others.

Uncle Brian is Wes's father and a responsible, safety-conscious adult on the trip. He balances allowing the children their independence with strict rules about survival, making sure they understand wilderness dangers, carry a satellite beacon, and file mapping itineraries.

Jake's father travels with his family to fulfill the park itinerary his own father designed. He holds fond memories of visiting the national parks as a child and serves as a chaperone, guiding the children while attempting to give them room to learn responsibility on the trails.

Jake's grandmother remains at home in Ohio while the family travels. She passes along her late husband's first puzzle clue and warns Jake to carefully protect the scrapbook, noting its immense value.

Abner is a middle-aged rancher in 1880s Colorado who takes Abe in when the boy needs shelter. He is a confident, established local who understands the dangers posed by aggressive investors trying to buy up the land. He hires Abe to help him build a new trail up Longs Peak.

Dunraven is an ambitious investor in 1880s Colorado who wants to take over the local territory. He and his partner chase Abe after the boy witnesses them burying a stolen silver spearhead.

Whyte works alongside Dunraven in 1880 to control the land around Estes Park and secure the silver spearhead. He aids in capturing Abe and later meets with Abner Sprague, only to be threatened with police action.

Hank is a wanderer in 1880 who knows the Colorado wild and the local Indigenous tribes better than anyone. He is a rugged, knowledgeable mountain man who shares the legend of the silver spearheads and their lunar origins with Abe over dinner.

Ranger Musgrave works at Rocky Mountain National Park. She provides Jake with a detailed topographical map and teaches him how to read its symbols, setting him up for success on his wilderness puzzle.

Jasper is an elderly man and a former ham radio contact of Jake's grandfather. He waits at a remote cabin in the park to deliver a heavy locked wooden box to Jake, operating under strict secrecy.

Mather is a covert associate referred to as the Keeper. He transported the heavy wooden box from New Mexico to Jasper a week before Jake's arrival, ensuring it reached the next step in its journey.

Stanley Ferguson is a man claiming to represent the Yellowstone National Park Improvement Company. He approaches Hank March in 1880 looking for the silver spearhead, leaving his business card behind in hopes of recovering the item.

Amber's parents travel with the Evans and Wes's families as part of the massive cross-country excursion. They help establish camp and agree to let the children explore independently under strict guidelines.