Well, to start with, Darion killed his father so that he could take over as king. Royal class shapeshifters are very difficult to kill, though, especially if you want it to look like a natural death, so he enlisted the help of a Hecate to provide him with the magic he would need to do so. His plans went awry, though, because he got cocky and figured that he didn't need the Hecate anymore and tried to go back on his bargain (he had promised her his first born child). She manipulated the king's guard so that they would discover Darion's plot, and so even though the king died Darion had to go into exile.
While in exile he met another Royal-class shapeshifter from another land named Dionysius and they fell in love. He had his first child, and so the Hecate came around looking for him. Darion's mate refused to allow her to take the newborn, and he was too strong for her to forcibly take him, so she settled for the fact that Darion would not be around to raise his son (after his mate discovered the pact he drove Darion away). The Hecate was content with the fact that she didn't really need that child so long as Darion could not influence him.
That child would grow up to be the main character, Daecon. His father Dionysius was forced to raise him among humans to hide him from Darion and from the shapeshifter colony. When Daecon grew up and discovered that he is a shapeshifter, he also discovered that he is a rare and powerful shapeshifter known as a Dunamis class (the Hecate knew he would grow up to be a Dunamis).
So Darion was not finished yet. As soon as Daecon made his first transformation the charms protecting him that had been cast by the Hecate broke, and Darion was now able to find Daecon. Unfortunately he found Daecon's friends first, and savagely attacked them with no provocation. Daecon intervened but not before Darion had killed one of his friends. That's two murders.
Later on Darion discovers that even though he murdered his father he is still king because the Shapeshifters had no laws disallowing his rule. He forcibly retakes his throne and immediately starts doling out punishment and revenge. He sentences the old Council of Elders to death, and then, when confronted, he murders Dionysius, his former lover. Murder number three.
Daecon witnesses this act and attacks Darion. Darion is quickly subdued, but Daecon turns away too quickly, giving Darion time to pull out a gun. He fires five shots at Daecon. Every one of the shots hit their target, but for some reason Daecon is unhurt. He finally subdues Darion once and for all. Rather than killing him and becoming a killer himself, he strips Darion of his magic and banishes him from shapeshifter society. Darion is upset that Daecon has punished him, but as Daecon said:
"You murdered your own father out of greed. You murdered my friend out of sheer cruelty. You murdered my father, your former lover, out of spite. And you tried to murder me out of cowardice. Of these facts there is no dispute. What could you possibly hope to achieve through a trial?"