That Last Onset — V.J. Chambers

Jason wants to punish himself for all the horrible things he's done, and so he's been lying low and wallowing in his guilt. When he discovers that Kieran and Eve are threatening his son, Chance, he finds Azazel so that the two of them can stop Kieran and Eve.

Kieran and Eve, now in possession of Jason and Azazel's powers, have the world in a chokehold. They see everything, know everything, and control everything. The only way to stop them is for Jason and Azazel to take back their powers.

But in order to do so, they must go through a series of tests, each pushing them deeper into their own darkness. If they get their power back, they run the risk of becoming the very evil they want to fight. But if they don't get the power, Kieran and Eve win and Chance is lost.