Angus Donohue doesn't want to be a warlock. He believes draining demons for magic is evil, but it's a dangerous opinion to have—his father is a powerful and well-connected warlock, and Angus is expected to follow the family tradition.
His only way out is to fail the demon summoning class. Failure means expulsion from the Warlock College. Despite Angus's best efforts to fumble the summoning, it works. Although not the way anyone expects.
Angus's demon, Saka, is a powerful mage with his own need for a warlock.
Saka wants to use Angus in a ritual to rebalance the magic that is being stripped from Demonside by warlocks. If Angus survives his demon's desires and the perils of Demonside, he'll have to face the Warlock College and their demands.
Angus must choose: obey the College and forget about Demonside or trust Saka and try to fix the damage before it's too late. Whatever he does, he is in the middle of a war he isn't qualified to fight.
Studies in Demonology book 1