The plot of Divine Divinity was a hero, who eventually becomes the Divine One, almost stopping the Black Ring's efforts to summon an aspect of the Lord of Chaos into a human baby. Unable to kill the baby (Damian) the Divine raises him as his son (between the events of DD and BD), determined to keep the demon suppressed, which worked great for 15 years, until Damian meet the beautiful Ygerna. The war that reshaped the land around Aleroth and ended with the Divine supposedly being killed was Damian getting revenge for the execution of Ygerna (for participating in Black Ring necromancy experiments on children).

can someone sum up the story

The only thing we know about the plot of Project E is that we will be able to defeat Damian.