BLACK STORM COMIN' WANTED: Young, skinny, wiry fellows not over eighteen. Must be expert riders. Willing to risk death daily. Orphans preferred.    When Colton Wescott sees this sign for the Pony Express, he thinks he has the solution to his problems. He's stuck with his ma and two younger sisters on the wrong side of the Sierra Nevada Mountains, with no way to get across. They were on the wagon train heading to California when Pa accidentally shot Colton and then galloped away. Ma is sick, and Colton needs money to pay the doctor. He'd make good money as a Pony rider. he also needs to get to California to deliver freedom papers to Ma's sister, a runaway slave. The Pony Express could get him there too...   Does Colton have what it takes to be a Pony Express rider? And if so, will traveling the dangerous route over the mountains bring him closer to family, freedom, and everything he holds dear?