Lentulus had plans to kill the Senate and set fire to Rome during the Saturnalia festival in December, and then take over the city during the ensuing chaos. He approached the ambassadors from the Allobroges, a Gaulish tribe, to ask them to help by starting a revolt in Transalpine Gaul. The Allobroges informed their patron in Rome, Quintus Fabius Sanga, who passed on the information to Cicero. On Cicero's orders, the Allobroges pretended to fall in with the plot and asked for more information. They were being taken to Catilina's camp by Titus Volturcius with letters of introduction, but instead they lead Titus Volturcius into a trap. Lentulus and other leaders of the conspirators, Gaius Cornelius Cethegus, Statilius, and Gabinius, were arrested and a meeting of the senate ordered that they be placed under house arrest in the houses of other senators while it was decided what to do with them. Crassus [www.suite101.com/article.cfm/18302/104269] was also accused of being involved in the conspiracy, but the Senate decided to ignore the testimony against him. Crassus himself spread the story afterwards that this evidence had been trumped up against him by Cicero.
The main speakers at the next meeting of the Senate were Julius Caesar, who was in favour of life imprisonment and forfeiture of the conspirators' property, and Marcus Porcius Cato and Cicero (in the fourth of his speeches In Catilinam), who favoured death. The senate voted in favour of the death penalty, and Cicero led the arrested conspirators one by one to the jail, where they were executed. When Catilina's forces heard of this, many of them deserted him. The remainder were defeated by Marcus Petreius, who was in command of Antonius' forces, since Antonius was ill at the time.
Although Cicero was hailed as "the father of his country" (pater patriae a title later used by Augustus), there were signs of trouble to come. It was possible to argue that his execution of Lentulus and the other conspirators was illegal in that execution of a citizen needed a vote of the whole people rather than just the senate. The counter argument was that the senatus consultum ultimum suspended the normal operation of law. Two of the new tribunes, who took office on 10 December while Cicero's term of office did not expire till 31 December, refused to allow Cicero to make any speeches to the people but only to take the oath customarily taken by consuls when their term expired. Cicero agreed, but changed the wording of the oath to include the fact that he had saved the country.
Towards the end of 62, news of a juicy scandal broke. A man was caught at the rites of Bona Dea (the Good Goddess), which were for women only, disguised as a woman. The man in question was Publius Clodius Pulcher, a young patrician (a descendent of the original Roman aristocracy) and the leader of a gang of street toughs who broke up public meetings that attempted to pass legislation Clodius disagreed with. His motive for sneaking into the rites of Bona Dea was said to be that he was in love with Pompeia, the wife of Julius Caesar, at whose house they were being held. Whether or not anything had happened between Clodius and Pompeia, Julius Caesar divorced her with the famous phrase that the wife of Caesar must be above suspicion. Clodius was charged with sacrilege, and at his trial he put forward an alibi that he was in Interamna, some 90 miles from Rome, that day. Cicero broke Clodius' alibi with evidence that he had met Clodius in Rome only three hours before the incident. Although Clodius was acquitted through wholesale bribery and intimidation of the jury, he never forgave Cicero.
Four years later, Clodius had his chance. In 59 he renounced his patrician status and had himself adopted by a plebeian (i.e., a non-patrician). He was now eligible for election as a tribune of the plebs, a post open only to plebeians. He was elected, and in 58 brought in a law that anyone who had put Roman citizens to death without a trial should be exiled. This was of course specifically aimed at Cicero's execution of Lentulus and the other Catilinarians. This was the time when Crassus, Caesar, and Pompey were the unofficial rulers of Rome in the league usually called the first triumvirate. When they first united they had invited Cicero to join them, but he refused, so they were in no mood to help him now.
Cicero went into voluntary exile and Clodius had a vote passed that no-one should give Cicero shelter within 500 miles of Italy. Despite this, many communities helped Cicero on his way to Greece. Although Cicero had said on his previous sojourn in Athens after his defence of Roscius that he would be perfectly happy staying there studying philosophy if he could not have a public career, now that the opportunity to live a life of study had arisen, it turned out that he could not wait to get back to Rome.