"The Intern" is a novel by Dmitry Grishanin, the fifth book of the eponymous cycle, in the genre RealRPG, urban fantasy.
They are here. They’re nearby. Sometimes within arm’s reach. They watch us. They’re always at the starting line. Their hunger is insatiable. And only the fragile barrier of equilibrium between almost-fused parallel worlds holds back hordes of otherworldly creatures.
Alas, sometimes breaches happen. And then the last obstacle between people and monsters becomes the teams of seers. A first-year student, Sergey Kapustin, who has been accepted as an intern into one of these teams, by order of his superiors begins searching for his escaped ally Marina—a former spawn/devil whose fragment of a dark soul, by chance, for a long time was "lodged" in the intern Kapustin’s body.
In the end, Sergey turns out to be a lousy detective—yet the bait from the guy is excellent. The hunter himself, unnoticed, turns into a victim and starts playing by the rules of the dark entity. The adventures continue.