When Gerard blinded Deucalion, one of his betas attempted to kill him to gain his alpha status. Deucalion killed him and discovered that when he killed him, his power transferred to himself. So he killed every last one of his betas. He then got the other alphas that were in Beacon Hills at the time to do the same. They then formed the Alpha Pack. While they were traveling, Deucalion found Aiden and Ethan. Deucalion saw potential in them so he wanted them as part of his perfect pack. They weren't being treated very well by their pack so he taught them how to control their shirt into one big wolf and they killed their alpha and took his alpha status and killed the remaining members of the pack, therefore joining the alpha pack.
Word got out that there was a new "True Alpha" and Deucalion wanted him as part of his pack. So they went back to Beacon Hills and, as cover asked Derek to join the pack. He refused as he had to kill his pack but after a while, it became clear that Deucalion wanted Scott not Derek. The Alpha Pack battled Derek's pack in an abandoned mall and Derek and Ennis fell off of the floor onto some stairs. Ennis nearly died but Deucalion finished him off. Kali was angry and went after Derek, forcing him to kill one of his betas, Boyd.
Deucalion finally persuaded Scott to go along with them for the time being but not as part of the pack. They went after the emissary, Morin Morrell but Scott stopped them form killing her. Kali and Aiden went after Derek when they fount he was gone, they went after each other before Jennifer appeared and killed Kali and killed the monster that the twins formed into. Scott and Deucalion waited for Jennifer who showed up with Derek. Everyone was rendered powerless when the lunar eclipse appeared and Jennifer took advantage and nearly killed Derek and Deucalion. As the lunar eclipse never lasted for long, Deucalion healed and so did Derek. Jennifer created a circle of mountain ash around herself. Scott broke the circle, becoming a "True Alpha". Deucalion slashed Jennifer's throat. Deucalion was then let go but as long as he didn't cause any trouble.