In the old West, many men got away with murder. Too few lawmen, too much hustle and bustle going on. This seemed the case in 1868 when a railroad contractor, Kane Kelly, shot a boy dead. Kelly fled the territory and that, most people thought, was that. But they didn't reckonon Detective N.K. Boswell of the Rocky Mountain Detective Agency. He promised the boy's family that he would bring the killer back to Laramie for trial. Boswell finds his man supervising a railroad crew in Iowa. But bringing him back to Laramie will be difficult and dangerous. Kane Kelly's brother Sligo is also ramrod of a railroad crew and with his gang of toughs he is determined to stop Boswell. He has plenty of opportunities; it's forty miles by buggy to the nearest railroad. Then there's the flooded Missouri River to cross, and four hundred miles of open prairie. Sligo tries brute force, using flunkies to do his dirty work. He tries bribery. He persuades a woman to seduce Boswell into a compromising situation. In the end, Boswell's legendary patience runs out. He lays a cunning trap, using his prisoner for the bait. If it works, Boswell will arrest Sligo Kelly, too. If it works.