It's 1861 and orphan Jo has made it from Carson City, Nevada, to San Francisco without anyone figuring out that she's a girl in boy's clothing. When she hears talk of gold strikes in the Cariboo, Jo and her friend Bart sign on for what turns out to be a journey far more arduous and dangerous than anything Jo experienced as a Pony Express rider. Through it all, Jo keeps her true identity a secret. Strong men turn back but Jo forges ahead, unsure of what lies ahead but sure that her father and mother would be proud of her determination.