Twelve-year-old Alf Smith trembled with excitement when the four cowboys rode past him as he walked home from school. This was Illinois farming country and he had never seen a real cowboy. The big Mexican saddles, the tall boots with the jingling spurs, and the pistols strapped on their sides, they were just like the Texas cowboys he had read about in books and newspapers. Alf hurried home to tell his parents, but his excitement soon turned to horror when he arrived to find the farmhouse engulfed in flames.
The story takes place in Wyoming territory in the 1870s. Will Roberts, a drifting cowboy wanders into the little sleepy town of El Dorado. He stops at the local saloon for a drink and maybe a tip on where he can find a job. While reluctantly sharing a table with a grubby stinky prospector he is drawn into a gunfight and saves the man's life. Salty, the prospector, rewards Will with half interest in his gold mine. Later that day will meets Victoria and falls madly in love with her.
Fleeing from murderous Apaches, Bo Logan finds a hidden valley in the Arizona desert but he also discovers a mystery that he can't ignore. Tom O'shay, a miner, has a cabin in the valley but he has vanished and his young daughter, Bonnie, is stranded somewhere in the slums of New York City. Bo must choose between courting Mary, his new-found love in Tucson, or traveling across the country and undertaking the almost impossible task of finding young Bonnie.
Alf Smith's adventures in El Diablo's Gold begins when he leaves the high plains of Texas and sets out to see the mountains of New Mexico. Along the way, Alf runs into more historical people, both good and bad, but he also meets a beautiful girl. The girl and her family are traveling along the El Camino Real back to their home in Mexico. Her father offers Alf a job guarding their coach. Alf takes the job because he is falling in love with the girl, but this will be the most dangerous and painful journey he has ever taken.