Driven from Rome by a deranged Marius, Sulla resorts to a truly drastic action -- he marches his army against Rome, drives Marius and his followers out, and seizes power by force. To describe this as shocking is a considerable understatement. Nothing of the kind had ever happened before in centuries of Roman history. It seems safe to say that it was probably as shocking to Sulla's contemporaries as such an event would be in the US today. Plutarch shows a distinct ambivalence toward Sulla's actions; McCullough does as well. One can readily understand why. The whole episode does credit to no one. Sulla is, after all, the lawfully elected consul and proper commander of the army in the field. Marius is aligning himself with a gangster and thug and seems to be motivated solely by ego and a desire for power. Plutarch also says that at this point Marius began his reign of terror (albeit on a smaller scale than it would later reach), executing Sulla's followers, i.e., the followers of the lawful consul and commander-in-chief. (McCullough omits this detail). So his overall behavior is appalling.
But so is the behavior of Sulla, who then marches an army against his own city, an unheard-of thing. Nor does he shine once he arrives. Plutarch reports that he threatened to burn houses down. McCullough actually downplays this, treating it as a bluff and says that he warned his soldiers not to commit any outrage against the Roman population, even executing one for looting. And he reasons with the people, pointing out that Sulpicius' measure expelling most of the Senate for debt is hardly compatible with any sort of debt relief and that Marius, though a great man (he takes care to express only praise for Marius) is in failing health and simply not up to the responsibilities of a command.
He then enacts major political changes that certainly appear to be historical, but that Plutarch does not so much as mention. Remember the post on Roman political institutions? Sulla made major changes that are revealing, both as to his social vision, and as to why enacting major changes to institutions is difficult -- because they have entrenched power and the capacity to defend themselves. McCullough reports (probably accurately) that Sulla phased in his changes strategically, starting with the least objectionable to disguise the full impact of what he was doing. First he suspended the usual requirement of an interval between when a measure was proposed and when it was enacted. Excusable, for a military commander in a hurry to go off and win his war. Next he repealed all Sulpicius' measures, again perhaps understandable in that they were enacted by violence. And he enlarged the Senate to make it functional again, a perfectly reasonable measure. But then his then he begins to move in a more alarming direction. First, he modifies the Centuriate Assembly (remember, the one divided into classes) to give nearly half of all power to the first class (the richest class). Next, he limits the tribal assemblies' legislative power to voting up or down on measures passed by the Senate. No longer can consuls or tribunes propose legislature to the assemblies without the Senate's permission, nor can they modify any proposal. Finally, he ends the tribal assemblies' authority to legislate at all and vests it solely in the Centuriate Assembly. In other words, he gets the tribal assemblies to vote away their own legislative power and vest it solely in an assembly controlled by Rome's richest class. It seems a safe assumption that they would not have done such a thing except in the presence of an army fingering its swords, with no threat openly made, but one clearly implied.
Consider, then what Sulla's new governmental institutions look like. The Senate, in addition to its old powers, has the sole power to initiate (though not to pass) legislation. Legislation will be voted up or down in the Centuriate Assembly, where only the richest class has any real power. This oligarchic assembly will also elect consuls, praetors, and censors, the only executive officials with real policy-making power. The Assembly of the Whole will be limited to electing tertiary executive officials whose powers are mostly administrative. The Plebeian Assembly will be limited to electing tribunes. Tribunes can no longer initiate legislation, but will still have the veto power. In short, what Sulla is making looks a lot like the narrow and tight oligarchy at the beginning of the Republic. And this is revealing as to his ultimate vision. It would suggest that what Sulla really wanted in the long run was not a dictatorship, but a narrow and tight oligarchy of a kind that had not existed in centuries. And Plutarch does not so much as mention any of these measures, although they must certainly have contributed to Sulla's unpopularity.
Finally, Sulla proclaimed a sentence of outlawry on a number of his opponents, including Marius and Sulpicius. They must flee or be killed. Sulla lets most of them escape, especially Marius who is too popular to kill, but he puts Sulpicius' head on a spike. Then he returns to the wars.
Naturally, all these measures make Sulla deeply unpopular. After the next election, all ten tribunes are opponents. Of the two consuls, Gnaeus Octavius is a supporter and Lucius Cornelius Cinna an opponent. Naturally, rivalry between these two consuls escalates and threatens to tear Rome asunder. Here Plutarch is hopelessly biased against Cinna and McCullough hopelessly biased against Octavius, so it is hard to tell exactly what happened. It appears that Cinna sought to reverse Sulla's measures and Octavius to maintain them. Both appear to have resorted to force. It seems most likely the Cinna resorted to force first, since, like the tribal assemblies before, the first class in the Centuriate Assembly would presumably not give up their lock on power voluntarily. McCullough has him attempt bribery instead -- offer to cancel debts if the Centuriate Assembly will reverse Sulla's measures. But given that they benefited from these measures, no matter how illegitimate and unconstitutional their enactment, it seems unlikely that Cinna could have hoped to get his way except by force.
Plutarch, on the other hand, describes Octavius as "a most excellent man [who] wished to rule in the justest way" and Cinna as "making war on the established constitution," a charge that would carry more force if Sulla had not just "established" the constitution at sword's point. Plutarch neglects to mention that Octavius sent armed followers against Cinna, who killed large numbers of citizens, or that he unconstitutionally deposed Cinna and the tribunes of Cinna's faction and sent them into exile. Once again, the whole episode resounds to no one's credit.
In exile, Marius and Cinna raise their own armies and lead them against Rome. All-out civil war ensues. Both sides offer citizenship to any non-citizen Italians who will support them. The Italians respond with a will. Marius trades on his popularity, but by now he has completely lost his mind and is surrounded by equally deranged ex-slaves who engage in wanton slaughter. Cinna, commanding a separate army from Marius, refuses to accept the warning from one of Marius' oldest friends (who is also a cousin) and from his own son that Marius is unstable and should not be trusted. (Does that seem likely? You would think that if a man's closest friends and his own son tell a distant acquaintance not to trust him, the distant acquaintance would take the warning seriously). Marius and his bodyguard seize Rome and launch a campaign of wanton slaughter until Marius has a stroke and dies. McCullough takes care to acquit Cinna of any complicity in the slaughter and portray him as a decent guy. Plutarch's description suggests that there may be some truth to the belief that Marius was deranged, at least during his final illness. But he does not dismiss the mad slaughter as simply the work of one deranged man; he full implicates Cinna and Marius' son in it as well. McCullough believes that the reign of terror ended when Marius died and his bodyguard was killed off. Plutarch says that it continued.
Clearly in the final chapters, things go from bad to worse quite quickly, as appears to be the case in real life. Just before his fatal stroke, Marius names the young Caesar flamens dialis, or high priest of Jupiter, nominally a great honor, practically, the end of any political or military career for him.
Unlike First Man in Rome, which ends with a sense of completion and seeming peace, The Grass Crown ends with things very much in the air. The Mithriditic War is still raging, and Sulla will not calmly accept what his enemies have done. We are left hanging.