Ol' Rosie, a cranky, old mare, has escaped the corral and has led ten of the Nolan's other horses into the stark mountains of eastern Oregon. It's not the first time, but for Wart's pa, this is a particularly desperate situation. On their ranch -- as on any ranch in 1907 -- horses are the key to a rancher's livelihood. So when Ol' Rosie and the other horses run off, somebody has to go catch them. But Wart's ma is having a baby. His pa needs to stay with her and to watch his little brother Danny. That leaves twelve-year-old Wart with the dangerous and critical charge of rounding up their runaway horses by himself.

Struggling through the rugged wilderness and facing almost overwhelming peril, Wart must keep his wits about him.

"I stood there for another minute trying to think. The wind had been knocked out of me but I was beginning to breathe better. I was miles from home. It was late afternoon -- soon to be dark. I was hurt. Gypsy was lame. Worst of all, I knew that the cougar was out there -- close to me. I was bleeding and he was hunting."

With each successive threat, Wart becomes more determined to defy the frightening odds against him and prove his worth to his stern, critical pa. Wart is sent on a mission to save his family's ranch, and along the way he learns that despite his youth and insecurity, he possesses the knowledge and spirit to survive and eventually triumph.