A young socialist by the name of Giacomo Matteotti threatened to unbalance Mussolini’s entire regime. In the Chamber of Deputies, he launched a verbal attack on Fascist violence, intimidation tactics, as well as on Mussolini himself. Matteotti despised fascism, and had travelled to Britain and Austria prior to this speech, trying to raise awareness of the true malignant nature of Mussolini’s regime.
Mussolini’s reaction was, predictably, one of severe anger, and he vowed to take his revenge on Matteotti. Realising that this was not a good way to handle the situation, he calmed down and gave a conciliatory speech, and won an ensuing vote of no confidence quite substantially.
This seemed to be the end of it, but 3 days later Matteotti disappeared, and his body was found 2 years later. Witnesses claimed the car that took him was that of Amerigo Dumini, head of the fascist ‘punishment squad’, and subsequently there was universal denouncement of Mussolini and the fascists.
Mussolini was in a very vulnerable position, and had his opposing parties put pressure on the king (who had the constitutional power to remove the prime minister) in a cohesive manner then Mussolini’s rule would surely have ended there. However, this was not to be, due to a massive misjudgement at the hands of the opposition parties.
What they thought to be a grand gesture, but was in fact a total and utter failure, was a display of purity in which they walked out of the Chamber of Deputies. This became known as the Aventine Secession, and with no opposition in parliament Mussolini was free to do what he liked, counting the oppositions seats as void because they had left, and giving them to pro-fascists.
Following this, Mussolini simply had to wait for the storm of protest to die down, which it did, and then he was able to resume as before. He made a bold speech on the 3rd of January in which he took responsibility for fascist crimes, claimed his innocence in the Matteotti affair, and vowed that the killers would be tried and punished. This was a clever move, and his promise to get tough with fascist radicals reassured a lot of Italian people, including liberals and conservatives, and the next vote in parliament he won decisively.