Longarm and the shotgun man

"Deputy U.S. Marshal Custis Long has had plenty of impossible missions. But his new undercover assignment riding shotgun for a robbery-plagued stagecoach line started out bad and quickly got worse. The gang he's after has four stolen stashes and four dead guards notched on its belt...and is gunning to make him number five. And the beautiful blond heiress he has to protect and the prissy city lady looking for excitement are only making Longarm's job twice as hard... Now the marshal and a coach full of innocent passengers are pinned down in a remote valley far from help. With time running out, the only chance Longarm has is to outshoot and outmaneuver the vicious gang in the deadliest showdown of his career..."--p. [4] of cover.