Founded by religious zealots, Arrarat's society is besieged by well-organized (and well-supplied) bandit gangs composed mainly of involuntary colonists. The story is a first-person narrative by newly-commissioned Lieutenant Harlan (Hal) Slater of the CoDominium Line Marines. Falkenberg commandeers him and any other available soldiers to form a provisional battalion to be sent to Arrarat in response to an urgent request for help from the governor. On arrival they find that they are not at all welcome. The governor had asked for a much larger (and more experienced) unit to deal with numerous lawless bands in control of much of the countryside. The military men have other concerns, however. They fear the havoc restless soldiers will create in the capital.
To avoid this Falkenberg elects to take the marines up-river to the bandit-occupied Fort Beersheba, an old fort built by the Line Marine regiment that had initially pacified the planet. Slater is tasked with taking and holding Fort Beersheba in a daring night assault using one company of airlifted troops, while Falkenberg marches the remainder of the newly organized 501st Line Marine Battalion up the river valley toward him. Holding the fort is not easy - though disorganized and untrained, the rebels have plenty of weapons with which to pummel Slater's A Company. Although A Company takes heavy casualties, Slater holds his position as the anvil to Falkenberg's hammer and the bandits attempting to flee from the CoDominium forces are destroyed.
After establishing the fort as a base, Slater and the other officers watch the restless and combat-eager marines suffer more and more from a military kind of cabin fever which they call the Bug. To combat this growing problem, Falkenberg forces the reluctant planetary governor to move against the bandits tyrannizing the farmers of the Jordan Valley who simply want to farm and be let alone by both the central government and the bandits gangs. Meanwhile Falkenberg directs a cleaning out of the farther reaches of the colony. However, the governor's campaign goes poorly and his forces are besieged in the town of Allansport, forcing him to call Falkenberg for help. Slater takes A Company to bait the enemy south of Allansport, and ends up holding off a major enemy counter-attack and occupying the strategic hill called the Rockpile, taking extreme casualties.
However, because of Slater's actions the enemy is defeated, with Slater severely wounded and medevacked to the capital.
However, the political situation is much more complicated. The religious farmers who had been oppressed by a gang of ex-convicts begin avenging themselves on anyone who collaborated with the bandits; while the colonial governor, who was trying to use the bandits to generate revenue to set up industries on Arrarat to provide employment for the time-expired convicts, becomes an enemy. How much of an enemy he will be is debatable, as he is in the Bronson camp and Bronson has no use for losers.
The story ends with the newly promoted Major Falkenberg recruiting the now Captain Slater (the youngest in the history of the fleet) into joining him in a transfer to Falkenberg's new command, the 42nd Line Marine Regiment, and Slater's Arrarat-born girlfriend Kathryn agreeing to join him.