Were the KMT and the Communist Party of China ever one single party in the 20's?

I know that the KMT is a nationalist party, but were the KMT and cpc ever one single party? It doesn't make any sense. Mao was a Communist, yet he was the propaganda director of the KMT... and how Chiang Kai-Shek plays into this as well boggles my mind too. If someone could clear the air on this it would be GREATLY appreciated, as I have a midterm on Tuesday, and I've got nothing.