Revolt at Fort Laramie

It's just prior to the Civil War and Fort Laramie's problem is the Sioux Indians. When it is announced that war has been declared the fort becomes divided between northerners and southerners. The fort Commander and the southerners resign and head south. But they have to go through Sioux territory and are soon attacked. A messenger gets back to the fort to relate their hopeless condition and the new northern commanded must decide what to do.